BI 206/216 Exam 1 Study Guide
BI 206/216 Exam 1 Study Guide BI 216
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This 9 page Study Guide was uploaded by JordanK on Saturday January 30, 2016. The Study Guide belongs to BI 216 at Boston University taught by Dr. Celenza in Spring 2016. Since its upload, it has received 170 views. For similar materials see Intensive Genetics in Biology at Boston University.
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Date Created: 01/30/16
BI 206/216 Study Guide Exam 1 Spring 2016, Dr. Celenza *** Covers class notes 1/19 1/28, textbook chapters 15 Chapter 1 double stranded macromolecule composed of 4 nucleotides (AT, CG) → stores genetic information genome : all of an organism’s genetic information, stored on chromosomes humans have 23 pairs (44 autosomal chromosomes and 2 sex chromosomes), which encodes for 25,000 genes (most of which are proteins) living organisms are distinguished from nonliving organisms by their metabolism, which is the ability to use energy Central Dogma : the information contained in DNA via the genetic code dictates the order of amino acids in proteins proteins are essential for all biological functions all living organisms use the same genetic code → evidence for common origin of all life certain genes exist are present in many organisms and encode the same function (ex: Pax6 genes for development of eyes) genes can be inserted in different organisms and produce the same product individual genome sequences can be analyzed to determine the genetic basis of many inheritable diseases gene function is determined through mutation → seeing what changes in an organism when mutation is introduced Chapter 2 before Mendel, artificial selectiowas used to breed offspring with desired traits used for animals (dogs) and food no one knew why sometimes traits would disappear and reappear in later generations Mendel used pea flowers to research genetics and inheritance easy to control fertilization, easy to grow large numbers quickly truebreeding lines produce offspring with specific traits that remain constant from generation to generation hybrids: offspring of genetically dissimilar parents (crossfertilization) monohybrid cross: crosses involving one trait discovered that some traits were dominant and some were recessive different types of same gene are calledlleles dominant trait iusually encoding for a functional protein while the recessive allelusually is encoding for a nonfunctional protein (or no protein at all) Law of Segregation says that the two parental copies of a gene in an individual separate during gamete formation and that gametes randomly unite during fertilization (one from each parent) use Punnett square to predict offspring genotypes & phenotypes product rule can be used to determine the probability of two or more independent events occurring together (event 1 and event 2) sum rule can be used to determine the probability of mutually exclusive events occurring (event 1 or event 2) Law of Independent Assortment: gene pairs independently assort; an AaBb individual could have AB/ab or Ab/aB gametes branchedline diagrams using product rule make it easy to predict outcome of offspring (especially with numerous genes) (taken from textbook, figure 2.17) Mendel’s Inheritance in Humans some defective alleles that cause disease are dominant (Huntington disease) while others are recessive (cystic fibrosis) pedigree : orderly diagram of a family showing relevant genetic features, used to determine if a disease is dominant/recessive and predict what offspring will inherit vertical patterns of inheritance = dominant horizontal patterns of inheritance = recessive Vocab phenotype: the observable characteristic homozygous : when an organism has 2 copies of the same allele (AA or aa) heterozygous : when an organism has 2 different copies of a gene (Aa) testcross : crossing an unknown individual with a known homozygous recessive individual to predict the unknown’s genotype if all offspring display dominant allele, unknown was homozygous dominant (single trait) if offspring are half dominant and half recessive, unknown was heterozygous (single trait) Chapter 3 a gene may have more than two alleles ex) blood type: A, B, and O alleles genes do not always display strict dominance/recessiveness Types of Dominance complete dominance: phenotype of dominant allele is completely shown incomplete dominance : phenotype of both allele is shown in a “blended” type of way ex) red and white flowers producing pink offspring interaction of two genes can produce nine different phenotypes for a single trait codominance : phenotype of both alleles are distinctly shown (Not blended) ex) blood type AB Mutations & WildType Alleles source of new alleles for a gene wildtype allele: the most common alleles in a population (often designated with a superscript “+”) at a frequency greater than 1% rare alleles are considered mutant allele frequency : the percentage that an allele of a gene accounts for of the total number of gene copies a gene can be polymorphic (multiple common wildtype alleles) or monomorphic (only one wildtype allele) One Gene May Contribute to Several Characteristics pleiotropy: a single gene can influence more than one characteristic ex) aboriginal Maori people of New Zealand have a defective protein that causes respiratory issues as well as being sterile ex) mutated HbS allele causes sicklecell disease but provides malaria resistance recessive lethal alleles: an allele that is dominant in function but recessive in lethality ex) coat color in mice AA = gray mice AAY = yellow mice AYA = dead mice (lethal) Y produces a 2:1 ratio of heterozygous AA to homozygous AA mice (fourth mouse dies) Two Genes Can Interact to Determine One Trait gene interactions can result in novel phenotypes ex) lentil color A_B_ = brown A_bb = tan aaB_ = gray aabb = green occurs due to different combinations of active/inactive enzymes interacting with each other complementary gene action: two enzymes (produced by two different genes) with their own separate biochemical reactions interacting to produce a given phenotype Epistasis epistasis: a gene interaction in which the effects of an allele of one gene hide the effects of alleles of another gene recessive epistasis : the allele which causes masking of other genes must be homozygous (because it is recessive) for the masking phenomenon to occur ex) labrador retriever coat color B_E_ = black bbE_ = brown __ee = yellow (doesn’t produce eumelanin) dominant epistasis : the dominant allele of one gene hides the effects of another gene often indicates that alleles of the two genes have antagonistic functions ex) squash & chicken color: dominant allele of gene B prevents deposition of a pigment whose synthesis depends on the dominant allele of gene A phenotypic ratios resulting from dominant epistasis (1 2:3:1 or 13:3) depend on the specific functions of the different alleles (copied from textbook, table 3.2) heterogeneous trait: a mutation at any one of a number of genes can give rise to the same phenotype ex) deafness breeding experiments (animals) and pedigree analysis (humans) can determine how a trait is inherited Same Genotype Does Not Always Produce the Same Phenotype penetrance : how many members with a given genotype show the phenotype complete (100%) or incomplete (ex: retinoblastoma has a penetrance of 75%) expressivity : refers to the degree or intensity with which a particular genotype is expressed in a phenotype ex) only one eye affected in retinoblastoma instead of two the environment can also have effects on phenotype ex) Siamese cats: colder areas of the body are darker in fur color certain traits are also determined by multiple alleles of several genes Chapter 4 Meiosis/Gamete Formation alleles are randomly separated from each other during gamete formation contributes to genetic diversity diploid (2n) → haploid (n) chromosomes in a fertilized egg are half parental and half maternal gametes randomly unite during fertilization structure of a chromosome two sister chromatids attached at center (centromere) pairs of chromosomes: homologous pairs karyotype : picture of stained chromosomes in homologous pairs of decreasing size cell cycle checkpoints must be passed to progress through cell cycle know basic steps in mitosis/meiosis (DNA replication, prophase, prometaphase, metaphase, anaphase, telophase; meiosis I/meiosis II) leptotene: first definable stage of prophase I; long, thin chromosomes begin to thicken, attached at a centromere zygotene: chromosomes begin matching up with homologous partner, matching chromosomes become zipped together (“synapsis”) pachytene: homologous chromosomes are united along their length, known as either “bivalent” (2 chromosomes) or “tetrad” (4 chromatids) crossing over occurs at this point diplotene: gradual dissolution of zipper complex, homologous chromosomes begin to separate except at sites of crossing over (“chiasmata”) diakinesis: further condensation of the chromatids; chromosomes can be distinctly seen Sex Chromosomes sex determining mechanisms vary greatly between species XX/XY female/male in humans, ratio in fruit flies can even be environmentallydetermined (ex: turtles) some genes are located on sex chromosomes ex) eye color gene is located on X chromosome xlinked (males with recessive X gene will display white eye color because Y chromosome has no effect hemizygous) BI 206/216 Notes (Spring ‘16) Class Notes 1/19 through 1/28 Intro phenotype: sum of an individual’s inherited traits and the influence of the environment; overall appearance genetics is the study of inheritable traits and the analytical methods used to study it “central dogma” is that DNA encodes proteins preMendelian genetics included b lended inheritance (ex: light green parent + dark green parent = medium green parent) → disproved theory Mendelian Genetics Mendel used peas to control mating, used cleancut traits in purebreeding lines, did reciprocal crosses and used large populations observed 7 characteristics that had only 2 phenotypes (no “blending”) which showed one trait was dominant over the other in a monohybrid cross, a consistent ratio of dominant recessive phenotypes (3:1) was observed led to the idea that each parent has lleles of the phenotype AA, Aa, or aa Law of Segregation: 2 alleles for each trait separate during gamete formation at random; 2 gametes (one from each parent) unite at random during fertilization can get omozygous genotypes (AA, aa) or eterozygous genotype (Aa) increases genetic diversity in a population testcross: crossing an unknown individual with a known homozygous recessive individual to predict the genotype of the unknown individual based on what the offspring are Current Genetics units of inheritance described by Mendel are calleenes pairs of antagonistic traits (A, a) are alleles of the same gene meiosis and segregation of alleles cause random inheritance → genetic diversity dominant allele =wild type (sometimes indicated with a superscript “+”) common allele in a population, serves as a benchmark for comparison many alleles of the same trait may all be wildtype Mendel’s 2nd Law Mendel’s Law of Independent Assortment alleles separate independently of each other during gamete formation ex) AaBb parent could form AB, Ab, aB, or ab gametes two AaBb parents produce offspring that show a 9:3:3:1 phenotypic ratio (9 showing both dominant, 3 showing only A dominant, 3 showing only B dominant, 1 showing both recessive) multiply expected ratios of each trait to predict ratios of phenotypes for a multitrait cross (multiplication rule) use addition rule to predict probability of one of several mutually exclusive events cystic fibrosis: recessive mutant allele fails to function as a chloride transporter which leads to excess mucus build up Interactions between Alleles of a Gene AA is chemically distinct from Aa, even if the phenotype is the same ex) amylopectin in peas (causes round shape) → Rr peas produce half as much as RR peas, even though both types appear round complete dominance : dominant alleles cause hybrids to only show dominant phenotype (ex: purple is dominant to white flowers) incomplete dominance : hybrid shows phenotype that looks like a blend of the two alleles (ex: purple x white parents = light blue offspring) codominance : hybrid shows discrete areas of both alleles in phenotype (ex: distinct patches of purple and white in same flower) seen in blood type → IAor I encode for slightly different glycosyltransferases while i has a single deletion of a nucleotide leading to a nonfunctional protein; blood type can be A, B, AB (*codominance), or O pleiotropic: one gene can affect more than one phenotype/characteristic ex) HbS allele that causes sicklecell anemia also provides resistance to malaria organisms who are heterozygous for a recessive lethal allele will always have offspring in a2:1 ratio in a monohybrid cross (recessive offspring will die) some genes may be dominant and recessive lethal at the same time ex) AA = dead offspring; AA = AYcoat color, AA = A coat color Epistasis the effects of one gene on another gene (masking, amplification, etc.) ex) hair genetics in humans → B/b determines color, H/h determines presence of hair in the first place B_H_ = brown hair bbH_ = blonde hair B_hh = alopecia (hairless) bbhh = alopecia affects Mendel’s expected 9:3:3:1 ratio in a dihybrid cross ex) lentil color: A = tan, B = gray, AB = brown, ab = green (no pigment, just chlorophyll) complementary gene interaction: both genes phenotypes are required to produce overall phenotype ex) both enzymes A and B in flowers are required to be purple, otherwise flowers are colorless (white) creates a 9:7 ratio in a dihybrid cross for phenotype because the mutant allele for each gives the same phenotype recessive epistasis: the recessive allele of one gene will mask the other gene, no matter what the allele is ex) labrador retriever coat color → BB/Bb is black fur, bb is brown fur, but both need EE or Ee to work because ee will produce yellow fur no matter what creates a 9:3:4 ratio for phenotype dominant epistasis : dominant allele of one gene completely masks the effect of the other gene no matter what produces a 12:3:1 ratio or 13:3 ratio ex) 12:3:1 in squash: enzyme B will not produce color, even if enzyme A (yellow color) or enzyme a (green color) is working (need bb to produce color) ex) 13:3 in chickens: AA/Aa makes color, aa does not make color; BB/Bb will not deposit color but bb will deposit color redundancy : produces 15:1 ratio, different genes encode same function (only homozygous recessive aabb will produce different function) allele interactions and gene interactions can occur at the same time → leads to different phenotypic variations Mutant Genotype the same mutant genotype does not always result in the same phenotype incomplete penetrance: mutant or wild type phenotype will occur even though mutant genotype is predicted ex) Siamese cats have mutant allele for dark fur but it only works in cold temperatures (feet, ears, tail) variable expressivity : mutant genotype has varying levels of being expressed phenotypically Chromosome/Inheritance sex determination is superficially similar between species but mechanistically different humans: XX = female, XY = male fruit flies: 1:2 ratio of X chromosomes to pairs of autosomes = male, 1:1 ratio of X chromosomes to pairs of autosomes = female (0.51 = intersex) homogametic sex in some reptiles and birds is male (ZZ), while heterogametic sex is female (WZ) *opposite of humans different systems exist for different species Mitosis & Meiosis chromosomes contain both DNA and proteins karyotype : image of all the chromosomes of an organism cell cycle contains G1, S, G2, and M phases M phase: prophase, prometaphase, metaphase, anaphase, and telophase cytokinesis involves cleavage furrow in animals and also the splitting of the cell plate in plants checkpoints must be passed between phases: pass based on nutrient availability, amount of damage, and/or need for new cells meiosis: 2n → n crossing over occurs in this process → increases genetic diversity one sister chromatid from each pair in each new gamete (4 gametes) *know terms from figure 4.15 in textbook about different stages in meiosis Drosophilia short life cycles (~1 week) good for genetics experiments involved in discovery of sexdependent phenotypes ex) red or white eye gene located on X chromosome
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