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Bio 240 Final Concepts Exam Study Guide!

by: Izabella Nill Gomez

Bio 240 Final Concepts Exam Study Guide! Bio 240

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Hey guys! So with the last exam coming up (drum roll, please) I have compiled ALL of my notes from the entire semester. These include detailed information from Dr. Hughes' lecture as well as inform...
General Genetics (Bio 240)
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This 85 page Study Guide was uploaded by Izabella Nill Gomez on Friday December 4, 2015. The Study Guide belongs to Bio 240 at University of Tennessee - Knoxville taught by Dr. Hughes in Summer 2015. Since its upload, it has received 298 views. For similar materials see General Genetics (Bio 240) in Biology at University of Tennessee - Knoxville.


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Date Created: 12/04/15
Biology 240 Final Concepts Exam Study Guide!  Biology 240 Chapter 2 Notes! DNA is organized into chromosomes and virtually all cells within the individual contains the same nuclear genetic material. Gene regulation determines gene expression. In eubacteria such as E coli, genetic material is present as a long circular DNA molecule compacted in an unenclosed nucleoid. Extends to a large part of the cell and does not undergo extensive coiling, nor is it associated extensively with proteins. They do contain genes specifying rRNA. The remainder of a eukaryote within the plasma is the cytoplasm, containing colloidal material called the cytosol, encompassing cellular organelles. Contain tubules and filaments, composing of cytoskeleton to provide support structures consisting of microtubules, which are composed of protein tubulin and microfilaments, derived from the protein actin. It maintains the shape and facilitates mobility for the cell, anchoring organelles. The endoplasmic reticulum compartmentalizes the cytoplasm, increasing surface area. The ER is smooth where fatty acids and phospholipids are synthesized; in others rough because of ribosomes. Ribosomes are sites where genetic information in mRNA is translated into proteins. Mitochondria are found in most eukaryotes and are sites of oxidative phases of cell respiration. It generates ATP. Chloroplasts (mostly found in plants) are associated with photosynthesis. Both contain DNA in a form distinct from the nucleus; it is also capable of duplicating, transcribing and translating its own genetic information. They closely resemble prokarya. These organelles were once primitive free-living organisms that established a relationship with primitive eukaryaendosymbiont hypothesis. Centrioles, located in centrosomes, are associated with spindle fibers that function during cell division. The organization of spindle fibers by centrioles occurs early in mitosis/meiosis and plays a role in movement of chromosomes as they separate during cell division. They are composed of microtubules consisting of tubulin. Each chromosome contains a constricted region of the centromere which establishes the appearance of each chromosome. Somatic cells derived from the same species contain the same number of chromosomes, representing a diploid number (2n). With the exception of sex chromosomes, these exist in pairs; members of each pair being homologous chromosomes. There are exceptions like bacteria, viruses, certain plants, yeast, mold (for they live haploid for most of their life). Humans have 2n number of 46 chromosomes. Each of the 46 is a double structure consisting of 2 sister chromatids connected by a centromere. Haploid number (n) is equal to half of the diploid. The genetic information contained in the haploid set of chromosomes constitutes the genome, which includes a copy of all genes including noncoding ones. Homologous chromosomes have identical gene sites, called loci (singular: locus). These are identical in traits and genetic potential. In sexual organisms, one member of each pair is derived from ovum and sperm. Each diploid organism contains two copies of each gene as bi-parental consequence/inheritance, which come from both parents. Members of each pair of genes can influence each pair of genes that are not identical. Alleles are different versions of the same gene. During meiosis, the diploid number of chromosomes becomes haploid. Gametes or spores contain 1 member of each homolog pair-1 complete haploid set. Fusion re- establishes the diploid set and becomes a zygote. Constancy of genetic material is thus maintained. In many species, one pair of homologs, sex-determining chromosomes are often not homologous in size, centromere placement, etc. (Ex: X and Y chromosomes). Multicellular diploid organisms begin life as single-celled fertilized eggs (zygotes). The mitotic activity of the zygote is the foundation for development and growth of the organism. In adults, mitotic activity is the basis for wound healing and cell replacement. Karyokinesis is the partition of genetic material into daughter cells during nuclear division. Nuclear division is very exact; results in the production of daughter nuclei with exact same chromosome composition. This is followed by cytokinesis where it parts and splits the plasma membrane. As the cytoplasm is reconstituted, organelles replicate themselves and arise from existing membrane structures or synthesized de novo in each cell. The cell cycle is the continuous alternation between non-division and division. The events in between constitute the cell cycle: Interphase: the initial stage of the cell cycle, the interval between divisions and includes the replication of DNA in each chromosome. G ∧G S Phase: DNA synthesis before mitosis. 1 2 are gap phases in which no DNA is synthesized. It includes the metabolic activity, cell growth and cell differentiation. By the end of G 2 , the cell has doubled in size and DNA has been replicated. G G Mitosis begins. During 1 cells either enter the 0 stage or proceed through G1 G0 . Those in do not proliferate. Prophase: characterized by migration of centrioles to the ends of the cell outside the nuclear envelope. Centrosomes organize microtubules into spindle fibers, creating an axis on which the chromosome separation occurs. Fungi, plants, and some algae lack this. The nuclear envelope begins to break down and the nucleolus to disintegrate. Chromatin fibers begin to condense. Two parts of each chromosome are called sister chromatids because DNA in each is genetically identical. These are held together by cohesin. The molecular complex formed between and during the S Phase is when DNA is replicated. The next stages are leg by migration of the chromosomes; which in turn are led by centromere regions to the equatorial plane/metaphase plateperpendicular to the axis established by spindle fibers. Prometaphase is the period of chromosome movement and metaphase is applied to the chromosome configuration following immigration. Migration is possible by the binding of the spindle fibers to the kinetochore, an assembly of multilayered proteins associated with centromeres. This forms on opposite sides of each paired centromere in association with sister chromatids. Once attached the cohesin is disintegrated by separase and sisters disjoin except at the centromere. The protein family of shugoshin protects cohesion from being degraded at the centromere. Mutations of the kinetochore proteins can potentially lead to errors during chromosome migration along the diploid content of daughter cells. Kinetochore microtubules from spindle fibers lengthen and shorten as a result of addition or reduction of polarized tubulin subunits. They each have one end near the centrosome region and another at the kinetochore. Anaphase is the event critical to chromosome distribution and the shortest stage of mitosis. Sister chromatids of each chromosome disjoin in disjunctionpulled to opposite ends of the cell: 1. Shugoshin must degrade 2. Cohesin must be cleaved by separase 3. Chromatids must go to opposite end of the cell. Each migrating chromatid is now a daughter chromosome. Movement is dependent on the kinetochore-spindle fiber attachment. Results from motor proteins. Molecular motors use energy generated by hydrolysis of ATP, and its effect shortens spindle fibers, drawing chromosomes to opposite ends. Steps in anaphase are critical. In human cells, there would be 46 chromosomes at each pole of the cell, one from each sister pair. Telophase: the final stage in mitosis. At the beginning, 2 complete sets of chromosomes are at each pole. The most significant event is cytokinesis, partitioning of the cytoplasm. In plant cells, the cell plate is synthesized and laid down across the region of the metaphase plate. Animal cells undergo constriction of the cytoplasm, the cell plate in plants is laid down and becomes the middle lamella. Primary and secondary layers of the cell as are deposited between the membrane and m. lamella in each daughter cell. In animal cells, constriction produces a cell furrow. Chromosomes begin to uncoil, the nuclear envelope reforms, spindle fibers disperse, etc. The cell enters Interphase. Cell division cycle (cdc) mutations: Normal products of many mutated genes are kinases that can add phosphates to other proteins. Some act as a “master control” molecules functioning with the protein cyclin. Cyclin binds to kinase activating at times during the cycle. Then it phosphorylates to other target proteins that regulate the process of the cell cycle. Cdc mutations help establish 3 checkpoints in the cycle: G1/S checkpoint: monitors cell size and condition of DNA. If DNA is damaged or growth is inadequate, progress is arrested. If adequate, the cell moves into Synthesis. G2/M checkpoint: DNA is monitored prior to mitosis. If replication is incomplete or if DNA is damaged, the process is arrested. M checkpoint: Occurs during mitosis, successful spindle fiber formation and spindle fibers to kinetochores necessary. Meiosis: Crossing over results in genetic exchange between members of each homologous pair of chromosomes. Sexual reproduction reshuffles genetic material; major source of recombination within species. Early in meiosis, homologous chromosomes form pairs, synapsis. Each synapsed structure, bivalent, gives rise to tetrad, composed of 4 chromatids, demonstrating both homologs duplicated. First division in meiosis I is reduction division. Components of each tetrad separate into dyads, which are composed of 2 sister chromatids joinder at the centromere. Second division in meiosis II is equatorial division. Each dyad splits into 2 monads of once chromosome each. Both divisions produce 4 haploid cells. Prophase I: same as mitosis except each homologous pair of chromosomes pair through synapsis, crossing over occurs. 5 substages: leptonemia, zygonema, pachynema, diplonema, diakinesis. Leptonema: interphase; chromatin material condenses, chromosomes visible. Along each chromosome are chromomeres, localized condensations resembling string. Homology search precedes and is initial pairing of homologs, begins during leptonema. Zygonema: chromosomes continue to shorten and thicken. Rough pairing complete at end of zygonema. During meiosis, lateral elements along chromosomes increases and synaptonemal complex begins to form between homologs. It is the vehicle responsible for proper alignment during pairing of homologs. In diploids, synapsis acts in zipper-like fashion, beginning at ends. Upon completion, homologs are referred to as bivalents. The number of bivalents equals the haploid number. Pachynema: chromosomes continue to coil and shorten, and the development of the synaptonemal complex continues between 2 members of each bivalent. This leads to synapsis, and referred to as a tetrad. Diplonema: apparent tetrad has 2 pairs of sister chromatids. Each pair begins to separate, but some areas remain intertwined (chiasma) at a point of crossing over. Diakinesis: chromosomes pull apart, but non-sister chromatids remain loosely associated at the chiasmata. The chiasmata move to end of the tetrad in separation. Terminalization begins at later diplonema and completed in diakinesis, in the nucleolus and nucleus breakdown; two centromeres of each tetrad form spindles. By the end of prophase I, the centromeres are present on the metaphase plate. Metaphase I: terminal chiasmata hold non-sister chromatids together, tetrad interacts with spindles, alignment of each tetrad is random. Half of the tetrad will be pulled to one end of the pole. Anaphase I: cohesin is degraded between sister chromatids, except at centromere. . The dyad is then pulled to each pole, disjunction occurs. When separation is not achieved, nondisjunction occurs. Telophase I: reveals nuclear membraned forming around the dyads. In this case, the nucleus enters a short interphase. If it occurs, the chromosomes do not replicate because they already have two chromatids. In others, they enter meiosis II. Much shorter than mitotic telophase. Meiosis II: essential if each gamete/spore relieves one chromatid from each original tetrad. Prophase II: each dyad has 1 pair of sister chromatids attached to the centromere. Metaphase II: centromeres positioned on metaphase plate. Anaphase II: occurs when shugoshin is degraded and sister chromatids pull apart. Telophase II: results in 4 haploid gametes, each chromosome being a monad. Spermatogenisis: takes place in testes, enlargement of an undifferentiated diploid germ cell-spermatogonium. Grow into a primary spermatocyte, which undergoes the first meiotic division. Products: secondary spermatocytes, which contain a haploid number of dyads. They undergo meiosis II for spermatids and spermiogenesis to become sperm. To become sperm, there must be equal amounts of cytoplasm when dividing. Oogenesis: same process as spermatogenesis, but there are not equal amounts of cytoplasm in each cell. Most occurs in the primary oocyte that is derived from the oogonium which is concentration in 1 of the daughter cells. Necessary for nourishment of the embryo. In the first polar body of telophase I, most of the cytoplasm is in the secondary oocyte, which then divides to become an ootid and second polar body. These divisions may not be continuous like sperm. The second meiotic division of the secondary oocyte produces a mature ovum. Biology 240 Chapter 3 Notes! Transmission genetics: study of how genes are transmitted from parents to offspring. Derived directly from Mendel’s experimentation. 1856-Mendel performed first set of hybridization experiments with garden pea. Continued until 1868. Traits: contrasting forms of an organism-characteristics are visible features. Mendel used these to compare garden peas in experimental fertilization. Monohybrid cross: cross involving only one pair of contrasting traits. Done by mating true-breeding individuals from two parent strands, each exhibiting one out of two contrasting forms of character in study. First generation examined, ton of offspring selfing: self-fertilization. Parental generation ( P1¿ : original parents. First filial generation (1 ): offspring of Parental Generation. Second filial generation ( F2 ): offspring of selfing. Ex: breed between tail and dwarf plants. Genetic data usually expressed/analyzed in ratios. Reciprocal crosses: when patterns of inheritancefrom one trait (sperm) and the other (egg) are the same no matter who fertilized. Ex: results of Mendel’s peas are not sex-dependent. To explain, unit factors for each trait are applied and serve as basic units of heredity unchanged from generation to generation. Mendel’s Postulates: 1. Unit factors are in pairs: genetic characters are controlled by unit factors existing in pairs of individual organisms. In a monohybrid cross, the specific unit factor for each trait. Each diploid receives one from each parent. Ex: 2 for tall, 2 for dwarf, one of each. 2. Dominance/recessiveness: when two unlike unit factors responsible for a single character are present in an individual, one unit is dominant to the other. Traits that are not usually expressed are recessive. Ex: tall-D, dwarf-R. 3. Segregation: During formation of gametes, paired units separate/segregate randomly so one of each gamete receives with equal likelihood. Ex: probability for tall and dwarf traits. Phenotype: physical expression of a trait. Gene: units of inheritance (unit factors). For any given character (such as height), the phenotype is determined by the alternative forms of a single gene; alleles/ Genotype: alleles written in pairs to represent unit factors. Designates genetic makeup of an individual. By reading the genotype, we know the phenotype (dominant/recessive traits). When both alleles are the same, they are homozygous. When the alleles are different, they are heterozygous. Test cross: method used to distinguish the genotype. Organism with a dominant phenotype but unknown genotype is crossed with a homozygous recessive individual. Dihybrid cross: two factor cross that analyzes 2 characters simultaneously. Best thought of as 2 separate monohybrid crosses. Ex: Yellow and green seeds independent of round and wrinkled. Product law of probabilities: when two independent events occur simultaneously, probability of two outcomes occurring in combination is equal to the product of their individual probabilities of occurrence. Ex: (3/4)(3/4)=9/16--- ¾ should be yellow, ¾ should be round. Independent Assortment: during gamete formation. Segregating pairs of unit factors assort independently of each other. Stipulates segregation of any pair of units occur independent of others. As a result, each gamete receives 1 member of every pair of units. For 1 pair, factor does not influence segregation of others. All combinations should be in equal frequency. Mendel’s 9:3:3:1 ratio/dihybrid ratio: ideal ratio based on probability that events involve segregation, independent assortment and random fertilization. Actual results are unlikely to match the ideal. Trihybrid cross: segregation and independent assortment applies to this 3-factor cross as well. In this, all individuals produced are heterozygous. Another method developed--fork-line method/branch diagram. Each gene pair is assumed to behave independently during gamete formation can be used for any number of gene pairs, provided all gene pairs sort independently from one another. For two or more gene pairs: 1. Determine the number of different heterozygous gene pairs (n) involved in the cross. Ex: AaBb x AaBb (n=2), AaBBCcDd x AaBBCcDd (n=3)---because B is not heterozygous. n 2. Once n is determined, 2 is the number of different gametes that can be 3n 2n formed, is the number of different genotypes of fertilization; is the phenotype from genotypes. Applied only if independently assorted. Continuous variation: held by students of evolutionary theory; describes offspring as a blend of their parent’s phenotypes. Ex: Darwin. Discontinuous variation: held by Mendel due to the dominant-recessive relationship of genes. Chromosomal theory of inheritance: deduced by Sutton and Boveri, the idea that genetic material in living organisms is contained in chromosomes. -Following independent segregation of each pair of homologs, each gamete receives one member from each pair. All possible combinations are formed with equal probability. Independent behavior of unit factors is due to separate pairs of homologous chromosomes. Chromosomes are composed of a large number of linearly ordered information containing genes. The location of any particular gene on a chromosome is called a locus. Different alleles of a given gene contain slightly different genetice information that determines the same character. Most genes have more than 2 allelic forms. Probabilities range from 0.0---certain not to occur---to 1.0----certain to occur. Product law: probability of 2 or more events occurring simultaneously is equal to the product of their individual probabilities. Sum law: calculation of probability when possible outcomes of 2 events are independent of one another can be accomplished in more than one way. The probability of obtaining any single outcome, where that outcome can be achieved by 2 or more events, is equal to the sum of the individual possibilities of the event. Binomial theorem: analyzes cases where there are alternative ways to achieve a n combination of events, a+b¿ =1 , a and b being probabilities of alternative ¿ outcomes and n number of trials. n! s t a b Ex: (s!)(t !) where n equals the number of trials, s the number one variable, t the same, and a and b is the probability of the outcomes of s and t. Mendel’s independent assortment and random fertilization is influenced by chance deviation, like observing the ratio of heads/tails coin. As the number of tosses is reduced, the impact of chance deviation increases--independent assortment and random fertilization is subject to random fluctuations from the predicted outcome due to chance deviation. As sample size increases, the chance deviation decreases. Null hypothesis: in observing deviation it assumes no difference between measured and predicted values. Any difference is chance. If rejected, the deviation observed is not due to chance. If not rejected, deviations are due to chance. Chi square analysis: test that assesses goodness of fit of null-hypothesis. Takes into account the observed deviation in each component of a ratio (expected) as well as 2 sample size and reduces to single number value x then estimates frequency of 2 x =ε d ε deviation: e where e is the expected value, the sum of each ratio 2 Interpreting x is evaluated by degrees of freedom (df)= n-1 where n is the number of different categories data is divided into. **The greater the number of categories, the more deviation by chance that is expected. x 2 Probability of value (p): form of interpretation of after df is determined. The percentage indicates the percentage expected for the experiment to exhibit the chance deviaton as great or greater than in initial, or less. Less=more chance More=less chance. The p-value should be less than .05 Pedigree: family tree that observes presence/absence of traits for each member. By analyzing the pedigree, allowed to predict how a trait is inherited. Consanguineous: related. -Siblings are in order of birth from left to right. Generations are in Roman numerals. Identical twins are monozygotic. Fraternal twins are dizygotic. An individual whose phenotype is brought attention to the family is proband. In albinism the synthesis of pigment of melanin is obstructed. Autosomal dominant diseases like Huntington’s is rare. If so, the parent always exhibits the trait, usually offspring too. Biology 240 Chapter 4 Notes! Gene Interaction: situation in which a single phenotype is affected by more than one set of genes. -Neo-Mendelian genetics investigates observations of genetic data that did not conform precisely to expected Mendelian alleles. Allele: alternative form of a gene. Allele that occurs most frequently (or is normal) is referred as the wild type allele(represented by a +, ex: abc+). It is often but not always dominant. **The process of mutation is the source of new alleles. For a new allele to be recognized by observation of an organism, the allele must cause a change in phenotype. A new phenotype is formed from a change in functional activity of cellular products specified by that gene. Loss of function mutation: causes a gene to create an enzyme that loses/reduces the affinity for substrate. A null allele results if loss is complete. Gain of function mutation: enhances the function of the wild-type product and increases the quantity of gene product. Results in dominant alleles. Ex:Proto- oncogens changed to oncogens, which override regulation of gene product. Function is always turned on. Neutral mutations cause no phenotypic change or evolutionary fitness change. -Traits are influenced by many gene products. Mutations can have a common effect in metabolic pathways―with a failure to produce an end product. Incomplete/Partial Dominance: no one gene dominates the phenotype. Creates an intermediate phenotype. There can be alleles that are neither dominant nor recessive. Haplo-insufficiency: when a single allele is not sufficient to produce the wild type phenotype and mask the other allele. (The dominant allele does not produce enough gene product/dose). Ex: red and white snapdragons― RR-red (anthocyamin-receives two doses)-1/2 rr-white (receives no doses of pigment)-1/4 Rr-pink (receives one dose of anthocyamin-not enough to make red)-1/4 1:2:1 ratio -Examination of gene product and activity often reveals intermediate gene expression (not in the phenotype). Tay-Sachs disease is related to lipid-storage deficiency. Those that are homozygous are affected, but heterozygotes are only partially affected. Threshold effect: normal phenotypic expression occurs any time a certain level of gene product is attained. In Tay Sachs, it is less than 50% of the time. Codominance: occurs when joint expression of both alleles occurs. 2 alleles of a single gene are responsible. Ex: MN blood group Both alleles expressed. -Codominant inheritance is characterized by distinct expression of gene products of both alleles. Different from incomplete dominance, where products of both alleles. Different from incomplete dominance, where heterozygotes express intermediate blended phenotype. -When mutation modifies information on a gene, each change produces a different allele. Multiple Alleles: when present in a population, inheritance may be unique. Multiple alleles can only be studied in populations―one organism may have at most 2 homologous gen loci coupled by different alleles of the same gene. Among members of a species, numerous alternate forms of the same gene can exist. Ex: ABO Blood Groups―characterized by the presence of antigens on the surface of red blood cells―different from MN antigens. Once combination exhibits co-dominant I IB forms of inheritance. for AB blood type are codominant to each other but dominant to i, (for O blood type). All individuals possess H substance, to which half of sugars are added (carbohydrates are terminal sugars that determine A or B blood type). Type O, unlike A, cannot add the H substance. -However, there are mutants of FUT1 gene that cannot express the sugar for the H substance even though they are type A or B functionally―Bombay Phenotype -Mutations resulting in nonfunctional genes can be tolerated in heterozygotes, where the wild type might be enough to produce the essential product. Recessive Lethal Allele: mutations resulting in a nonfunctional gene; lethal to homozygotes. May respond as phenotype in heterozygotes. Ex: yellow pigment in mice. Dominant in coat to wild-type, so heterozygotes are yellow. Homozygotes die before birth. A A −homozygousrecessive death ) A A−homozygous dominant agouti ) Y A A−heterozygote (yellow ) 2:1 ratio signals lethal gene Dominant lethal allele: the presence of just one copy of the allele results in death. Ex: Huntington’s disease: Delayed until adulthood in heterozygotes, that results in motor and neurological degradation. (Dominant lethal alleles are rarely observed). -For dihybrid corsses such as albinism risk and blood type, the 9:3:3:1 ratio converts to 2:6:3:1:2:1, establishing the probability of each phenotype. Phenotype in many cases is affected by more than one gene. Genetic influence on phenotype is more complex than Mendel’s encounters. Gene Interaction expresses the idea that several genes influence a particular characteristic. DOES NOT MEAN THAT TWO OR MORE GENES INTERACT DIRECTLY TO INFLUENCE. DOES MEAN THAT CELLULAR FUNCTION OF NUMEROUS GENE PRODUCTS CONTRIBUTES TO GENE DEVELOPMENT OF A COMMON PHENOTYPE. Epigenesis: a point in which each step of development increases the complexity of an organ or feature and is under the control/influence of many genes. Ex: formation of inner ear in mammals. Forms as a result of a cascade of intricate developmental events influenced by many genes. Mutations that interrupt these events leads to hereditary deafness. In a sense, many genes “interact” to produce a common phenotype. Mutant phenotype then becomes the heterogeneous trait. Epistasis: the expression of one gene pair masks/modifies the effect of another. Sometimes the genes involved influence the same general phenotypic characteristic in an antagonistic manner, which leads to masking. But other times, the genes involved exert influence on one another in a complementary fashion. Ex: recessive homogeneous allele (epistatic) may override the expression of other alleles (hypostatic) at another locus. 2 gene pairs may also complement one another such that at least one dominant allele in each pair is required to express a particular phenotype. (9:7 ratio or 9:3:4). **When a single character is being studied, a ratio of 16 parts (ex: 3:6:3:4) suggests that two gene pairs are “interacting” in the expression of the phenotype under consideration (epistasis has an effect of combining one or more of 4 phenotypic categories in various ways). Conventions: 1. In each case, a distinct phenotype classes produced, disassemble from others. Illustrate discontinuous variation―phenotypic traits are discrete and different from each other. 2. Genes considered in each cross are on different chromosomes and assort independently during gamete formation . Ex: A,a,B,b. 3. When we assume complete dominance (AA,Aa,BB,Bb) is equivalent to genetic effects of A- or B- (- means other alleles present) 4. P1 crosses are with homozygous individuals (AABB, aabb,AAbb, aaBB). Each F 1 has heterozygote (AaBb) F 5. 2 is the main focus. When 2 genes are involved, genotypes fall into 9/16 A-B-, 3/16 A-bb and 1/16 aabb. All genotypes are equivalent on the effect for the phenotype. Ex: mice A- agouti aa-black bb-a bb masks A or a alleles (recessive epistasis) F -Novel Phenotypes may be expressed in the 2 generation in addition to the F modified dihybrids Ex: squash shape. 1 = AaBb x AaBb (both disc). A-bb and aaB- yield sphere shape (new phenotype). (gene interaction) **When 16 in ratios of dihybrid crosses where inheritance pattern is unknown think 2 gene pairs involved. Heterogeneous trait: go back to hereditary deafness. Complementation analysis: allows to determine whether 2 independently isolated mutations are in the same gene (alleles) or represent mutations in separate genes. May reveal if only a single gene is involved in a mutation or multiple genes. Ex: Drosophila bugs F 1 generation. Case 1: All offspring have wings―2 recessive mutations (that make bugs wingless) in separate genes and not alleles―being heterozygotes, both genes have a normal copy of each gene and complement. Case 2: No wings―2 mutations affect the same gene and are alleles of one another. No complementation, homozygous for 2 mutant alleles. No normal product produced. Complementation group: is for all mutations present in a single gene. Complement mutations are in all other groups. Helps predict the number of genes involved in the determination of a trait. Pleiotropy: when a single gene has multiple phenotypic effects. Ex: Marfan Syndrome: results from autosomal dominant mutations in the gene encoding fibrillin. Also, Poryphyria variegate: does not allow for the metabolization of hemoglobin when the respiratory pigment is broken down. Leads to toxic buildup. -A major portion of the Y chromosome is inert genetically. There is only a small portion that is homologous to the X chromosome in order to separate during meiosis. X-linkage―genes present on the X chromosome exhibit patterns of inheritance different from those with autosomal genes. One of the first examples was the white eye of the Drosophila female, which was an X-linked mutation that was expressed in male offspring only. -Since the Y chromosome lacks homology with almost all genes on the X alleles present on the X will be directly expressed in the phenotype. Males cannot be homozygous or heterozygote for X-linked possession of only one copy of a gene in diploid is heterozygosity. One result of X-linkage is in a crisscross pattern, where recessive X-linked genes passed from homozygous mom to all males. Occurs because females express recessive mutant allele on both chromosomes. Ex: colorblindness. -If X-linked disorder debilitates/lethal to individuals prior to reproduction, disorder exclusively in males―only source of lethal allele in heterozygote female “carriers”. Pass on to ½ of males. Ex: Duchenne muscular dystrophy. -In sex-linked inheritance and sex-influenced inheritance: autosomal genes responsible for contrasting phenotypes but expression dependent on hormone constitution of the individual. So, heterozygotes may exhibit a phenotype in males and contrast in females. Ex: domestic fowl plumage distinctly different in males and females, demonstrating sex limited inheritance―controlled by a single pair of autosomal alleles modified by hormones. Sex influenced patterns of inheritance include pattern baldness in humans, horn formation in sheep and coat patterns in cattle. Autosomal genes are responsible, while trait may show in both sexes, expression dependent on hormone constitution. -Most gene products function within a cell, cells interact with one another in various ways. Organisms exist under diverse environmental influences. **Gene expression and resultant phenotype modified through interaction between individuals’ genotype and external environment. Degree of expression can be shown by determining penetrance and expressivity. Penetrance: Percentage of individuals that show at least some degree of expression of a mutant genotype. Ex: If 15% of flies have a mutant genotype with wild-type appearance, penetrance of mutant gene is 85% Expressivity: range of expression of mutant genotype. Ex: eyeless gene in flies can range from normal to partial to none―experiments show genetics and environmental factors influence expression. Position effect: effect of genetic background; where physical location of a gene in relation to other genetic material may influence expression. Ex: if a region of chromosome is relocated, normal expression of genes in that region may be modified more. True if gene is relocated to areas condensed and genetically inert (heterochromatin) Ex: white eye of X-linked Drosophila―if a region of X chromosome with w+ allele is relocated, caused red and white phenotype. -Temperature affects/influences phenotypes through chemical activity―dependent on kinetic energy. Ex: a primrose is red at 23 degrees Celsius and white at 18 degrees. Siamese cat and Himalayan rabbit-fur black in cold areas and white in warmer ones. (temperature sensitive mutations). These are rexamples of conditional mutations. Permissive conditions allow an organism to grow, restrictive conditions require and organism to use essential genes and arrests. Nutritional mutations are crucial in bacteria―mutations that prevent synthesis of nutrient molecules may kill microorganisms. They can also prevent organisms from metabolizing a substance Ex: lactose intolerance. -Some genes are expressed at different phases of life: prenatal, childhood, pre-adult and adult. Genetic Anticipation: a form of heritable disorders that exhibit progressively earlier ages of onset and increased severity of the disorder in each successive generation. Es: Myotonic dystrophy. -Genomic/Parental Imprinting: process of selective gene silencing that occurs during early development, impacting subsequent phenotypic expression. Impact depends on parental origin of genes/regions involved. Leads to direct phenotypic expression of allele(s) on homologs that are not silenced. Biology 240 Chapter 5 Notes! -Goals for Bio: DNA is organized into chromosomes which are units of heredity; chromosomes are segregated (you should be able to describe linkage and what it does to segregation ratios) Most chromosomes contain a large number of genes. Those that are part of the same chromosome are linked and demonstrate linkage in genetic crosses. Because chromosomes and not genes are the units of transmission in meiosis, linked genes are not free to undergo independent assortment. Instead, alleles at all loci are transmitted as a unit. In many cases, this does not occur. Crossing over or reshuffling/recombination shuffles alleles between genes and always occurs during the tetrad stage (prophase-the exact moment is still unknown). This is currently viewed as a physical breaking and rejoining process. The frequency of crossing over is proportional to the distance between genes. Chromosome maps indicate the relative locations of genes on chromosomes. Chiasma shows consequences of crossing over―exchange of material of 2 homologous chromatid segments. Genes on the same chromosome may be inherited together. Complete linkage produces only parental/noncrossover gametes. Two parental gametes are formed in equal proportions when genes are linked on the same chromosome and only two genetically different kinds of gametes are formed. Crossover between linked genes involves non-sister chromatids―this generates 2 new allele combinations―recombinant/crossover gametes. As distance between 2 genes increases, the proportion of recombinant gametes increases and parental gametes decreases. Recombination can occur between any 2 of 4 chromatids of a homologous pair. Genetically occurs between sister chromatids. The only way to tell if recombination has occurred in homologous chromosomes is if the alleles are different. If complete linkage exists between 2 genes because of close proximity and F organisms that are heterozygous at both loci are mated, a unique 2 phenotypic ratio results―a linkage ratio. Ex: Drosophila; hv-heavy wing vein (mutant recessive) hv+-thin wing vein (wild type) bw-brown eye(mutant recessive) bw+-red eye (wild type) 1:2:1- one heavy wing, 2 wild type, 1 brown eyed When large numbers of mutant genes in a species are investigated, genes on the same chromosome are linked―linkage groups can then be identified (one for each chromosome). Genes on a single chromosome comprise a linkage group (there are 24 linkage groups in the human genome (22 autosomes, 2 sex chromosomes)). The number should correspond to the haploid number of chromosomes. Alternate possibilities of genetic recombination―independent assortment. unlinked linked partially linked (like unlinked) Crossing over indicated by × -Morgan( who discovered X linkage) postulated that linked genes are arranged in a linear sequence along the chromosome and that variable frequency of exchange occurs between any 2 genes during gamete formation. 2 genes relatively close to each other alonge a chromosome are less likely to have a chaisma form between them than if the 2 genes are farther apart on the chromosome. The closer the genes are, the less likely that an exhacne will occur between them. The frequency of crossing over(recombination) between 2 genes is proportional to the distance between the genes. Ex: Drosophila; rate of occurrence for phenotype 1. Yellow, white.5% → sum of 1 and 2=3 **Recombination frequencies between linked 2. white, minute 34.5% genes are additive 3. yellow, minute 35.4% The distance between yellow and white is .5 (mu-map units) and the distance between yellow and minute is 35.4 mu. The distance between white and minute is 35.4-.5=34.9 mu X-linkage and crossing over are not restricted to the X chromosome, but can apply to autosomes. In Drosophila, there is more crossing over in females than males. -During meiosis, a limited number of crossover events occur in each tetrad. These recombinant events occur randomly along the length of the tetrad. The closer that two loci reside along the axis of the chromosome, the less likely that any single crossover event will occurs between them → occurs between 2 nonsister chromatids, but not the two loci that are being studied. Where two loci are far apart, crossover does occur. When crossover occurs, the other two chromatids of the tetrad are not involved. These are used to determine the distance between two linked genes. The percentage of tetrads involved in an exchange between 2 genes is 2x as great as the percentage of recombinant gametes produced. Theoretical limitation of observed recombination due to crossing over is 50%. Double exchanges of genetic material result from double crossovers (DCOs). 3 genes pairs must be investigated to do this. 2 independent and separate events/exchanges must occur (refer to the product law). Ex: single crossover between A and B is 20% (p=.20); B and C is 30% (.30). The chance of a double crossover is (.20)(.30)=.06 or 6%. Double exchanges of genetic material are used to determine the distance between 3 linked genes. Genes must be heterozygous for both alleles. A test cross is used to test whether an organism is a heterozygote or homozygote for certain traits. Ex: Aa × aa (all linkage studies use this to study recombination in a heterozygote) 1:1 ratio Class Question: If no crossing over occurs between these two, what phenotypes result? pr-purple eyes pr+-wild type vg- vestigial wing vg+-wild type Answer: Wild type pr and vg recessive Class Question: If crossing over does occur, what phenotypes? Answer: wild type, purple vestigial (recessive), vestigial (wild type) and purple eye **If a trait is not specifically stated, assume wild type Class Question: If the genes are unlinked? Answer: wild type, purple vestigial (recessive), vestigial and purple eye For a successful mapping cross: 1. The genotype of the organism producing the crossover must be a heterozygote at all loci under consideration. 2. The cross must be constructed so genotypes of all gametes can be accurately determined by observing phenotypes of the resulting offspring. 3. A sufficient number of offspring must be produced. To diagram a 3 point cross successfully, ** we must assume some theoretical sequence, even though we do not yet know if it is correct. Ex: Drosophila; white eye, yellow body, echinis eye shape. P1 -males hemizygous for all 3 wild type; females homozygous-recessive F1 -females are heterozygous, males hemizygous recessive F2 F1 - females and males will express genotype from -To create a chromosome map, we must determine which F2 phenotypes correspond to noncrossover and crossover categories. For noncrossover in F 2 phenotypes, we must identify individuals derived from parental gametes from the F1 female. Each such gamete contains an X chromosome unaffected by crossing over. Genotypes of parental gametes and F 2 phenotypes complement one another. Ex: if one is wild type, the other is a mutant for all 3 genes. In other situations, if one chromosome shows a mutant allele, the second shows the other two mutant alleles―these are the reciprocal classes of gametes and phenotypes. -2 noncrossover phenotypes are most easily recognized because ** they occur in the greatest proportion of offspring. -The 2nd category is easily represented by double-crossover phenotypes, ** present in the least numbers. -The remaining categories for the 4 phenotypic classes result from single crossovers. Double crossovers represent 2 simultaneous single crossovers. To determine gene sequence (Method I): 1. Assume any of the 3 orders (w-y-ec, y-ec-w, y-w-ec), then determine the arrangement of alleles along each homolog of the heterozygous parent giving rise to noncrossover and crossover gametes. 2. Determine whether a double-crossover even occurring within the arrangement will produce the observed double-crossover phenotypes (which occur least frequently). 3. If this order does not produce the correct phenotypes, try each of the other 2 orders. Method II: assumes that following a double crossover event, the allele in the middle position will fall between the outside/flanking alleles that were present on the opposite parental homolog. Interference (I): the inhibition of further crossover events by a crossover event in a nearby region of the chromosome causes the reduction. To quantify discrepancies that result from interference, we calculate the coefficient of coincidence (C): observed DCO C= expected DCO . To quantify interference: I=1-C. If interference is complete and no double crossovers occur, I=1 . If fewer DCOs than expected occur, I is positive and positive interference has taken place. If more DCOs than expected occur, negative interference has occurred. Positive interference is most commonly observed in eukaryotes. Lod score method: helps to demonstrate linkage of 2 genes when they are separated to the degree that recombinant gametes are formed. Assesses the probability that a particular pedigree involving 2 traits reflects genetic linkage between them. A value of of 3 or above indicates linkage―-2 or below does not. If → the result is between -2 and 3 inconclusive. DNA markers: short segments of DNA whose sequence and location are known, making them useful for mapping purposes. Ex: Cystic Fibrosis ― a gene located using markers. Sister chromatid exchanges: occur during mitosis, do not produce new allelic combinations. Frequency of SCEs significant but unknown why. Cis and Trans configuration: The way alleles of a gene are organized on chromosomes Cis configuration: Trans configuration: Crossover depends on whether mother is cis or trans! Cis crossover: Trans crossover: Suppose: P1 AABB x aabb F 1 AaBb If A and B genes are linked, the offspring has Cis configuration If the genotype of the offspring is recombinant: If A and B are trans, the parental crossover of the offspring looks like this: Ab **In linkage studies, you are really looking at meiosis of the mother P 1 Noncrossover gametes: y+ ec+ y ec y ec Crossover gametes: y+ ec ** Difference between unlinked genes and linkage y ec+ with crossing over: crossing over is much rarer than noncrossing over To determine the distance of genes: divide the sum of crossovers by the total number of offspring to get the percentage. Ex: there are 10,000 flies for offspring. To find the percentage of noncrossover gametes: [275+273]/10000= .05 or 5% (created numbers). Percent crossover is equivalent to the crossover map units. Biology 240 Chapter 25 notes! -Evolution is a consequence of changes in genetic material through mutation and changes in allele frequencies in populations over time. Union of population genetics with the theory of natural selection is neo-Darwinism. Speciation: formation of new species. It is facilitated by environmental diversity. If a population is spread over a geographic range encompassing a number of ecologically distinct subenvironments with different selection pressures, populations occupying these areas may gradually adapt and become distinct from one another. These may remain in existence, continue to diverge or become extinct or reunite with other populations. Populations that are reproductively isolated are different species. Microevolution: evolutionary change within populations of a species. Macroevolution: evolutionary events leading to the emergence of new species and new taxonomic groups. -Variation in Homo sapiens is low, only 9% because of race, 6% because of geographic location Population: group of individuals belonging to the same species that live in a defined geographic area and actually or potentially of a population. Most populations contain a high degree of heterozygosity. One way to determine if genetic variation exists in a population is artificial selection, if little to no variation, artificial selection will have no effect on the phenotype; if genetic variation present, phenotype will change over a few generations. Ex: domestic dog. Gene pool: all alleles in a population and the genetic information that the members carry. -There is an enormous reservoir of genetic variability in populations; alleles representing these variations are distributed among members of a population. -Variations between populations reflect the product of local adaptation or geographic isolation. Variation among homologous DNA sequences---single nucleotide polymorphisms. There are approximately 1 million human SNPs(single base pair mutations-these are detected by microarray(dots are the binding of SNPs and hybridized)). -Some SNPs are inherited from crossing over in meiosis. -Microsatellites are areas where there a short repeated segments (can be used as DNA markers). Ex: CACACA. It the DNA sequence is known on either end of the repeat, the repeat can be PCR amplified. Microsatellites can expand and contract. **Mutations are inherited. Neutral theory: of molecular evolution; proposes that mutations leading to amino acid substitutions are usually detrimental, with only a very small fraction being favorable. Some mutations are neutral--functionally equivalent to replaced allele. Favorable/detrimental ones are preserved/eliminated by natural selection. The frequency of neutral alleles in a population is determined by mutation rates and random genetic drift---not selection. Some neutral mutations will drift to fixation, others will be lost. Diversity of alleles at most loci doesn’t reflect action of natural selection, but is a function of population size (larger--more variation). Other explanation for high genetic variation is natural selection. Some enzyme or protein variations are maintained by adaptation. Ex: sickle-cell anemia heterozygotes to malaria. -Neutral theory points out that some genetic variation is expected simply because of mutation and drift; and studies reason for molecular evolution. -Changes in allele frequencies in a population that do not result in reproductive isolation are examples of microevolution. Hardy-Weinberg Law: describes what happens to allele and genotype frequencies in an “ideal” population that is infinitely large and randomly mating, not subject to evolutionary forces such as mutation migration or selection: 1. Frequencies in alleles in gene pool do not change over time 2. If two alleles at a locus A and a are considered then after one generation of random mating, frequencies of AA:Aa:aa in populations can be calculated as p +2pq+q =1 where p=the frequency of allele A and q=the frequency for a. It is rare for any population to be in Hardy-Weinberg . In Hardy-Weinberg, all genotypes have equal rates of survival and reproduction. In next generation, all genotypes contribute equally to the new gene pool. Chi-square can be used to check whether deviations from the expected frequencies are larger than expected. If the deviation is larger than expected, one or more Hardy-Weinberg assumptions are being violated. Assumptions of Hardy-Weinberg: 1. Individuals of all genotypes have equal rates of survival---no selection 2. No new alleles are created by mutation 3. No individuals migrate into or out of the population 4. Population is infinitely large, no sampling error 5. Mating is random -By specifying conditions under which the population does not evolve, Hardy- Weinberg can be used to identify real-world forces that cause allele frequencies to change. Application of this model can reveal “neutral genes” in a population gene pool not operated by forces of evolution. -Hardy-Weinberg shoes that dominant traits do not necessarily increase from one generation to the next. Second, it demonstrates genetic variability can be maintained in a population since, once established in an ideal population, allele frequencies remain unchanged. Third, knowing the frequency if one genotype allows to calculate all other genotypes at that locus. It is useful to calculate the frequency of heterozygote carriers for recessive disorders. According to Hardy-Weinberg, 2 2 genotype frequencies are predicted to fit p +2pq+q =1 relationship. If they do not, one of the assumptions or more have been violated. -Hardy-Weinberg can be used to calculate allele frequencies for X-linked traits. The frequency of X-linked alleles in the gene pool and the frequency of males expressing the X-linked trait is the same. Natural selection: individuals of a species exhibit variations in phenotype--difference in size, agility, coloration, etc. Many of these variations are passed on to offspring. Organisms tend to reproduce in an exponential fashion; more are reproduced than can survive. This causes a struggle for survival; in this struggle, individuals with particular phenotypes will be more successful than others, allowing the former to survive and reproduce at higher rates. -Weak selection may just involve a fraction of a percent difference in survival rates. Fitness: individual organisms’ genetic contribution to future generations. Genotypes with high rates of reproductive success have high fitness. -A homozygous recessive individual that has died before reproduction has a fitness W=0. Selection against deleterious alleles show frequency of allele decline with q =¿ g frequency of allele in generation g q =¿ q = q0 0 starting frequency of allele g 1+gq 0 g=¿ number of generations passed -There is a rapid decline of the allele, then a plateau to be expected because the homozygotes have been eliminated and heterozygotes are present (not selected against). As more time passes, the elimination is slower. As long as heterozygotes mate, it’s difficult to eliminate the deleterious recessive allele. -For selection to produce rapid changes in allele frequencies, differences in fitness among genotypes must be large. -Phenotype is the result of combined influence of the individual’s genotype at many different loci and the effects of the environment. Directional selection: phenotypes at one end of the spectrum present in the population become selected for or against, usually as a result of changes in the environment. Ex: Galapagos finches’ beak size, bacterial resistance. Stabilizing selection: tends to favor intermediate phenotypes, with those at both extremes being selected against. Over time, it reduces the phenotypic variance. Ex: human birth weight. Disruptive selection: selection against intermediates and for both phenotypic extremes. Opposite to stabilizing selection. -Within a population, the gene pool is reshuffled in each generation to produce new genotypes in offspring. Allows for new genotypic combinations. ** Assortment and recombination do not produce new alleles. Mutation: alone acts to create new alleles. Mutational events occur at random. For dominant mutations: 1. The allele must produce a distinctive phenotype that can be distinguished from similar phenotypes produced by crossover alleles. 2. The trait must be fully expressed/completely penetrant. 3. Identical phenotypes must not be produced by non-genetic agents (drugs, chemicals). -Mutation rates can be stated as the number of new mutant alleles per given number of gametes. Migration: occurs when individuals move between populations. Migration can change the frequency of an allele by breeding with another population from the same locus. pi 1−m )pi+m p m ' pi=howmigration affects frequencyof theallele m= migrants from mainland to island and migration is random pm =frequency of allele on mainland pi¿ frequency on island -change in allele frequency is attributable to migration is proportional to the differences in allele frequency between the donor and recipient populations and to p p the rate of migration. If m is large or m is different from i , a large change in frequency of that allele can occur in a single generation. If migration is the only acting force, equilibrium will be attained when pip m Genetic drift: in small populations, significant random fluctuations in allele frequencies are possible by change alone. The degree of fluctuation increases as population size decreases. Drift can also arise through the founder effect, which occurs when a population originates from a small number of individuals. Genes carried by all members derive from the founders (like homozygous cheetahs). Drift can also arise via genetic bottleneck. Develops when a large population undergoes a drastic but temporary reduction in numbers. Even though the population recovers, genetic diversity is greatly reduced. Ex: Navajo Indians with albinism. -Nonrandom mating can change the frequency of genotypes in a population. Subsequent selection for or against certain phenotypes has the potential to affect the overall frequencies of the alleles they contain, but it is important not that nonrandom mating ** does not itself directly change allele frequencies. Positive assortive mating: similar genotypes are more likely to mate than dissimilar ones. Ex: humans are attracted to people that resemble themselves. (not selected for ABO blood groups, MN, etc---they follow Hardy-Weinberg). Negative assortive mating: dissimilar genotypes are more likely to mate. Ex: plants that cannot self-fertilize so they cross-pollinate. -Nonrandom mating changes genotype frequency but not allele frequency. Changes phenotype of individuals. Inbreeding has most commonly found to affect genotype frequencies. Occurs when mating individuals are more closely related than any two individuals drawn from the population at random. Inbreeding increases the proportion of homozygotes in a population. Coefficient of inbreeding, (F), quantifies the probability that the alleles of a given gene in an individual are identical **because they are descended from the same single copy of the allele in an ancestor. If F=1, homozygous; F=0, no individual has two alleles derived from a common ancestral copy. Species: a group of actually or potentially interbreeding organisms that is reproductively isolated in nature from all other such groups. In sexually reproducing organisms, speciation transforms the parental species into another species, or divides a single species into two or more. **Genetic divergence of populations with considerable genetic variation present as differences in alleles/allele frequencies can reflect the action of natural selection, drift, or both. Sympatric speciation: process through which new species evolve from a single ancestral species while inhabiting the same geographic region. Allopatric speciation: occurs when populations of the same species become isolated from each other to an extent that prevents or interferes with genetic exchange. Different geographical ranges are occupied. **The most common form of speciation. Once migration stops, species form. Reproductive isolating mechanisms: are biological barriers that prevent or reduce interbreeding between populations. Prezygotic isolating mechanisms prevent individuals from mating (unable to by some reason). Prezygotic isolating mechanisms create reproductive isolation even when two members are willing to mate. Viability/fertility may be reduced, or hybrids are sterile. Others: -Ecological -Behavioral -Mechanical -Physiological -Seasonal Average time for speciation is 100,000 years but can occur in a much shorter time span. Ex: cichlids in in Nicaragua. Phylogeny can be used to determine the evolutionary history of a species by establishing the relationships between them. Can be constructed by amino acid sequences through the sequence of cytochrome C, a mitochondrial protein that has changed slowly over time. Genetic equidistance: differences in amino acid sequence between species and major groups is proportional to evolutionary distance. Minimal mutational distance: nucleotide changes necessary for all amino acids. Differences in a protein are totaled. Molecular clocks: measures the rate of change in amino acid or nucleotide sequences in species. Ex: Africans provide the highest levels of diversity from original Homo sapiens. Non-africans originated 50,000 years ago. Neanderthals 30,000 years ago (coexisted with sapiens, are 99.7% identical). Possible test questions: -The parental frequency of a generation is M=.5. If the population is in Hardy- Weinberg equilibrium, the frequency of the next generation will be: M=.5. Is the population evolving? No. -Given allele that results in disease state in humans may nevertheless be propagated in populations because: the disease has a late onset, the individual is heterozygous for the disease and the wild type has a selective advantage. -In assertive mating there is a: deficiency of heterozygotes. Biology 240 Chapter 6 notes! -Bacteria and their viruses have extremely short reproductive cycles. They can also be studied in pure culture---single species or mutant strain of bacteria or one type of virus can be isolated and investigated independently of other similar organisms. Bacteria are essential to studies due to their easy manipulation and generation of solid results for researchers. -Genetically homogeneous bacteria cultures can give rise to cells with inheritable variation under unique environmental conditions. Adaptation hypothesis: implies that the interaction fo the phage and bacterium is essential to acquisition of immunity. Exposure “induces” resistance. Spontaneous mutations: occur regardless of the presence or absence of bacteria--- phage T1 is another alternative to the resistance of E. coli. Fluctuation tests mark initiations of modern bacterial genetic studies. Mutant cells that arise can be isolated by selection, culturing organisms under conditions where only the desired mutants grow well. Bacteria are usually haploid, so all mutations are directly expressed in the descendants. Bacteria are grown either in liquid or a semi-solid agar surface. Minimal mediums contain only one organic carbon source +¿ +¿,K ¿ (glucose/lactose); various inorganic ions such as ¿ , etc. can be added as −¿,Na¿ Cl well. To grow on the medium, bacteria must be able to synthesize all nutrients, being prototrophic (wild type). The mutant that cannot synthesize one or more nutrients is an auxotroph. A complete medium has been extensively supplemented with nutrients an auxotroph might not be able to synthesize. If indicated by a minus sign (-) after a nutrient/amino acid, the auxotroph cannot metabolize/synthesize the chemical. If an antibiotic is present with an r, the bacteria is resistant; if with an s, the bacteria is susceptible and cannot resist the antibiotic and survive. -The growth pattern of bacteria: Lag phase: slow Log phase: period of rapid (exponential) growth, cells divide continually 10 9 Stationary phase: reached when the cell density is maximized to about cells/mL in a petri dish. Genetic recombination here refers to th


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