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Lectures 30-38 notes

by: Anna Perry

Lectures 30-38 notes BIOSC 0150 Zapanta - Foundations of Biology 1

Anna Perry
GPA 3.5
Foundations of Biology 1

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An outline of the book chapters in the lectures mixed with important things Zapanta said in lectures. This is useful for test 4
Foundations of Biology 1
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This 23 page Test Prep (MCAT, SAT...) was uploaded by Anna Perry on Tuesday February 3, 2015. The Test Prep (MCAT, SAT...) belongs to BIOSC 0150 Zapanta - Foundations of Biology 1 at University of Pittsburgh taught by Zapanta in Fall2015. Since its upload, it has received 98 views. For similar materials see Foundations of Biology 1 in Biology at University of Pittsburgh.


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Date Created: 02/03/15
Lectures 30 amp 31 The Cell Cycle Ch 1214 I How Do Cells Replicate Cell division is the process by which existing cells divide to form new cells There are two types Meiosis leads to the production of gametes eggs and sperm and the daughter cells have half the amount of genetic material as the parent cell Mitosis leads to the production of all other cell types somatic cells ie Body cells and daughter cells are genetically identical to the parent cell Replication is accomplished by cytokinesis the division of cytoplasm Mitosis and cytokinesis are responsible for three key events in eukaryotes 1 Growth need more cells for larger size 2 Repair replacing damaged cells 3 Asexual reproduction When cytokinesis is complete a parent cell has given rise to two new daughter cells A cell s genetic material DNA is organized into chromosomes Chromosomes contain a single long double helix of DNA wrapped around proteins called histones n eukaryotes this DNAprotein material is called chromatin Each of the DNA copies in a replicated chromosome is called a chromatid Chromatids from the same chromosome are sister Chromatids Chromatids are joined together at the centromere A 7 A Sister AV Chromatids 7 A 39 Chromosome Heplicalli m Centromere wjg Chromosome Chromosome replication Growing cells cycle between two phases a dividing phase called the mitotic phase and a nondividing phase called interphase Chromosome replication occurs during interphase in the S phase Two gap phases exist during which no DNA synthesis occurs but organelles are synthesized and additional cytoplasm is made This ensures that the daughter cells will have the organelles they need and be normal in size and function The gap between M and S is the G1 phase The gap between S and M is the G2 phase The cell cycle consists of four phases M phase lnterphase made of O 61 o S O 62 5 DNA synthesis cw l mu Chromosomes are replicated in S phase and divided into daughter cells in M phase II What Happens During M Phase At the start of mitosis each chromosome consists of two sister chromatids attached to each other at the centromere During mitosis the two sister chromatids separate to form independent daughter chromosomes One copy of each goes to each daughter cell Mitosis is a continuous process with ve subphases 1 Prophase Chromosomes condense and the mitotic spindle apparatus microtubules begins to form Chromosomes rst become visible in this phase The spindle apparatus is a structure that produces mechanical forces that move replicated chromosomes during early mitosis and pull chromatids apart in late mitosis It is made of microtubules called spindle bers 0 Polar microtubules push the poles of the cell away from each other causing the cell to elongate o Kinetochore microtubules pull chromosomes to the poles of cell causing movement The spindle bers originate from a microtubule organizing center MTOC o In animals l centrosome 0 Each centrosome contains a pair of centrioles During prophase in animal cells the spindle begins to form around the chromosomes by moving centrosomes to opposite sides of the nucleus 2 Prometaphase The nuclear envelope dissolves and microtubules attach to chromosomes Kinetochore microtubules from each mitotic spindle attach to sister chromatids of each chromosome 0 Attachment occurs in the centromere region at the kinetochore 0 Each sister chromatid has its own kinetochore o Kinesin and dynein motors on the kinetochores walk the chromosomes along microtubules Once kinetochores have attached to microtubules chromosomes begin to move to the middle of the cell 3 Metaphase Formation of the spindle is complete and chromosomes migrate to the middle of the cell As you get movement of spindle bers there is a tug of war that causes chromosomes to line up in the center on the metaphase plate 4 Anaphase Centromeres split and sister chromatids are pulled by the spindle bers towards opposite poles of the cell Two type of movement occur during anaphase 1 The daughter chromosomes move to opposite poles via the attachment of kinetochore proteins to the shrinking kinetochore microtubules o Microtubules shorten at kinetochore to pull daughter chromosomes apart 0 They shorten because tubulin subunits of the microtubules are lost from their plus ends at the kinetochore Dyneins and other kinetochore motor proteins are attached to the kinetochore s crown and walk toward the minus end of the spindle ber 2 The two poles of the spindle are pushed and pulled farther apart Repicated chromosomes split into two identical sets of daughter chromosomes 5 Telophase A new nuclear envelope begins to form around each set of chromosomes and they decondense Mitosis is complete when two independent nuclei have formed quotl x l9 Cytokinesis typically occurs immediately after mitosis The cytoplasm divides to form two daughter cells each with its own nucleus and complete set of organelles In plants polar microtubules left over from the spindle help de ne and organize the region where the new plasma membranes and cell walls will form 0 Vesicles are transported to the middle of the dividing cell and fuse to form a cell plate In animal cells cytokinesis occurs when a ring of actin and myosin laments contracts inside the cell membrane forming a cleavage furrow Control of the Cell Cycle Bacteria divide using binary ssion As a bacterial chromosome is being replicated protein laments attach to the copies and separate them to opposite sides of the cell 1 DNA is copied and protein laments attach 2 DNA copies are separated ring of protein forms 3 Ring of protein draws in membrane 4 Fission complete 5 Cell cycle length varies among cell types because of variation in length of 61 phase Gl phase is eliminated in rapidly dividing cells Nondividing cells are stuck in 61 phase 0 Enter an arrested stage called Go state Variations in cell cycle length suggest that it is regulated and that regulation varies among cells and organisms MPhase promoting factor MPF induces mitosis in all eukaryotes and is present in the cytoplasm of Mphase cells It consists of two subunits it s a dimer 1 A protein kinase called cyclindependent kinase Cdk Cdk is active only when bound to cyclin 2 A regulatory protein called cyclin The level of Cdk over time is constant and the level of cyclin increases during interphase reaching its peak when mitosis begins then decreasing during Mphase Cdk is further regulated by two phosphorylation events 1 After it binds to cyclin Cdk becomes phosphorylated at two sites making it inactive and allowing the concentration of the MPF to increase without immediately activating mitosis 2 Late in 62 enzymes dephosphorylate one of the phosphates on Cdk making it active and initiating mitosis There are cellcycle checkpoints in three phases of the cell cycle These are critical regulation points that allow a cell to decide whether or not to proceed with cell division Prevent cell division of damaged cells or mature cells in Go 1 The rst and most important checkpoint occurs late in 61 Four factors affect whether it will pass i Cell size ii Nutrient availability iii Social signals from other cells iv Health of DNA 0 The p53 protein regulates the cell cycle in 61 if DNA is damaged It can activate genes that stop the cell cycle until the DNA damage is repaired If not it initiates apoptosis or cell death 0 P53 is a tumor suppressor 2 The second checkpoint is between 62 and M Ces stop growing if chromosome replication has not proceeded properly or if DNA is damaged 0 This prevents the removal of the inactivating phosphate from MPF keeping it inactive 3 In M phase one checkpoint regulates the start of anaphase If chromatids are not correctly attached to kinetochores you could get two chromatids on one side and none on the other 4 In M phase another checkpoint regulates progression through anaphase If chromosomes do not fully separate MPF cyclins are not degraded and MPF remains active preventing the cell form exiting the M phase IV Cancer Out of Control Cell Division When cell cycle checkpoints fail uncontrolled growth can occun A mass of cells formed by uncontrolled cell growth is a tumor Benign tumors grow in a single location and aren t cancerous Malignant tumors are cancerous 0 Cells become malignant if they gain the ability to detach from the original tumor and invade other tissuesljmetastasis Cancers are thought to arise from cells with a defect in the 61 checkpoint Cancerous cells have two types of defects 1 Defects that make the proteins required for cell growth active when they shouldn t be 2 Defects that prevent tumor suppressors like p53 from shutting down the cycle Cells respond to signals from other cells and divide only when their growth bene ts the whole organism This is social control Social control is based on growth factors small proteins released by cells that stimulate division in other cells Rb is a tumor suppressor protein that prevents progression to the S phase 1 Growth factors arrive from other cells 2 Growth factors stimulate production of E2F and G1 cyclins which are different than those used in MPF 3 Rb binds to E2F inactivating it The G1 cyclins begin forming cyclinCdk dimers The Cdk is inactive phosphorylated 4 When dephosphorylation turns on the G1 cyclinCdk complexes they catalyze the phosphorylation of Rb Rb changes shape and releases E2F E2F is free to activated its target genes mu Lecture 32 Mitosis vs Meiosis Ch 122 amp 131 l Chromosomes Carry Genes Gametes are reproductive cells Sperm is a male reproductive cell Egg is a female reproductive cell The process of uniting sperm and egg is fertilization This forms a new individual and restores chromosome number 0 Forms a diploid zygote which develops through mitosis into an adult of the next generation Hapoid cells form egg or sperm cells via gametogenesis Meiosis is a nuclear division that leads to a halving of chromosome number and forms gametes The X and Y chromosomes are sex chromosomes and are associated with an individual s sex Nonsex chromosomes are autosomes Chromosomes that are the same size and shape are called homologous chromosomes or homologs Homologous chromosomes carry the same genes a section of DNA that in uences some hereditary trait in an individual 0 Different versions of a speci c gene are called alleles Homologous chromosomes carry the same genes but each homolog may contain different alleles The Concept of Ploidy A karyotype shows the number and types of chromosomes present Organisms that have two versions of each type of chromosome are diploid o Diploid cells have one paternal chromosome of each type and one maternal chromosome of eachtype Organisms whose cells contain one of each type of chromosome are haploid The letter 17 stands for the number of distinct types of chromosomes in a given cell and is the haploid number In humans 17 is 23 The combination of the number of sets and n is the cells ploidy Ploidy 7 2n 3n etc indicates the number of each type of chromosome present lnstead of having two homologous chromosomes per cell polyploid cells have three or more of each type An Overview of Meiosis Before Meiosis begins each chromosome in the diploid parent cell is replicated When complete each chromosome will consist of two identical sister chromatids attached at the centromere Meiosis consists of two cell divisions ln meiosis I the homologs in each chromosome pair separate from each other The diploid parent cell produces two haploid daughter cells 0 Outcome is a reduction in chromosome number known as a reduction division During meiosis ll sister chromatids from each chromosome separate The cells produced have one of each type of chromosome Phases of Meiosis l During Early Prophase I the nuclear envelope begins to break down chromosomes condense and the spindle apparatus begins to form The homolog pairs then come together in a pairing process called synapsis Synapsis is possible because regions of homologous chromosomes that are similar at the molecular level come together The structure that results is called a bivalent or tetrad o Held together by the synaptonemal complex During Late Prophase I the nuclear envelope breaks down and microtubules of the spindle apparatus attach to kinetochores Nonsister chromatids begin to separate but remain connected at the chiasmata The chiasmata mark sites where DNA was broken and rejoined between homologs early in prophase I This process of chromosome exchange is crossing over Elmer Ehii smatai hmmaildg r H Spindle ln Metaphase I the tetrads nish migrating to the metaphase plate Centramere kinetuehnrel Mier mbule marched to Hi EI GHIJTE ln Anaphase I the paired homologs separate and begin to migrate to opposite ends of the cell Stil each homolog consists of sister chromatids that are not identical but still connected at centromere Sister chromatids mmaiingatiauhe Homologuua Wei132 chrumuswmzne sepr39ailie In Telophase I the homologs nish migrating to the poles of the cell Then the cell divides in cytokinesis a Cleanrage urmw At the end of Meiosis I One chromosome of each homologous pair is distributed to a different daughter cell A reduction division has occurred The daughter cells are haploid but still in the form of sister chromatids V Phases of Meiosis Because no chromosome replication occurs between meiosis and II each chromosome consists of two sister chromatids at the start of meiosis During Prophase II the spindle apparatus forms and one spindle ber attaches to the kinetochore of each sister chromatid at the centromere n Metaphase II the chromosomes line up at the metaphase plate 1 In Anaphase ll sister chromatids separate and the resulting daughter chromosomes begin moving to opposite sides of the cell 147Jr n ln gt1 1 J In Telophase ll chromosomes arrive at opposite sides of the cell and a nuclear envelope forms around each haploid set of chromosomes Each cell undergoes cytokinesis At the end of Meiosis II There are four haploid cells Each has one daughter chromosome of each type in the chromosome set Lecture 33 Meiosis Ch 1323 Meiosis Promotes Genetic Variation Asexual reproduction is any mechanism of producing offspring that does not involve the production and fusion of gametes Based on mitosis Offspring produced are clones or exact copies of their parents Sexual reproduction is the production of offspring through the production and fusion of gametes Based on meiosis Leads to greater variation The changes in chromosomes produced by meiosis and fertilization are signi cant because chromosomes contain the cell s hereditary material Genetic variation is caused by in order ofincreasing variability 1 Random combination of egg and sperm outcrossing 2 Crossing over 3 Separation and distribution of homologous chromosomes independent assortment 0 When pairs of homologous chromosomes line up during meiosis and the homologs separate a variety of combinations of maternal and paternal chromosomes can result Humans have a haploid number of 23 which means that there are 223 84 million different combinations of chromosomes in gametes Crossing over is a form of genetic recombination the appearance of new combinations of alleles on the same chromosome These combinations did not exist in either parent Even with selffertilization gametes from the same individual combining offspring will be genetically different from the parent What Happens When Things Go Wrong in Meiosis Two things must occur for a gamete to get one complete set of chromosomes 1 Each pair of homologous chromosomes must separate from each other during meiosis 2 Sister chromatids must separate from each other and move to opposite poles during meiosis II If both homologs in meiosis or both sister chromatids in meiosis move to the same pole of the parent cell the products of meiosis will be abnormal This is nondisjunction because they fail to disjoin lf nondisjunction occurs in meiosis I daughter cells will be n1 n1 n1 n1 0 Cells that have too many or too few chromosomes of a particular type are said to be aneuploid o Trisomy is n1 Down syndrome is trisomy 21 o Monosomy is n1 lf nondisjunction occurs in meiosis ll daughter cells will be n n n1 n1 Lecture 34 Meiosis and Sexual Reproduction Ch 134 amp 501 Why Does Meiosis Exist There are three main mechanisms of asexual reproduction 1 Budding Offspring forms within or on the parent and breaks away when fully developed 2 Fission An individual splits into two organisms 3 Parthenogenesis The female produces an offspring without fertilization from a male Offspring are genetically identical to mother Eggs produced by mitosis OR meiosis Asexual reproduction is much more ef cient than sexual because no males are produced Daphina reproduce both sexually and asexually Throughout the spring and summer they produce only diploid female offspring by parthenogenesis In late summerearly fall females begin producing male offspring Haploid sperm produced in the males fertilize the eggs in females Eggs are released in winter and survive at the bottom of a lakepond In spring they hatch and begin reproducing asexually II The Purifying Selection Hypothesis Sexual individuals are likely to have some offspring that lack the deleterious alleles that are present in a parent Natural selection against deleterious alleles is purifying selection Reduces the numerical advantage of asexual reproduction Ill The Changing Environment Hypothesis If the environment changes offspring that are genetically different from their parents are more likely to survive and produce offspring than offspring that are genetically identical to their parents According to the changingenvironment hypothesis sexual reproduction increases the tness of individuals in certain environments IV Mechanisms of Sexual Reproduction Gametogenesis The mitotic cell divisions meiotic cell divisions and developmental events that produce gametes are called gametogenesis Spermatogenesis is the formation of sperm Oogenesis is the formation of eggs Occurs in the gonad Male gonads are testes female are ovaries Spermatogenesis occurs continuously throughout the male s adult life Dipoid cells called spermatogonia 2n divide by mitosis Some of the resulting cells continue to function as spermatogonia others change to form specialized cells that are committed to developing into sperm The specialized cells are primary spermatocytes 2n These undergo meiosis l and produce two secondary spermatocytes n which then undergo meiosis II The result is four haploid cells called spermatids n Spermatngnnium Mitosis l w ldditienal spermatogonia Primaryr spermatocyte First 5 it g a meldtle wt divisiun 2 Secondary v H spermatocytes 39 piece There are four components to the mammalian sperm The head contains the nucleus and acrosome which stores enzymes that allow the sperm to penetrate the barriers surrounding the egg The neck encloses a centriole that will combine with a centriole contributed by the egg to form a centrosome The midpiece is packed with mitochondria which produce ATP required to power movement The tail consists of a agellum which makes swimming possible In oogenesis the production of primary oocytes stops early in development in many mammals Dipoid cells called oogonia 2n divide by mitosis Some of the resulting cells continue to function as oogonia others change to form specialized cells committed to producing an egg The specialized cells that result are called primary oocytes 2n These cells undergo meiosis but only one of the haploid products known as secondary oocytes n can mature into an egg The secondary oocyte is arrested in the nal stages of meiosis ll until it is fertilized by a sperm it then completes meiosis to become an ootid n which matures into an ovum n The other 3 cells produced have a tiny amount of cytoplasm and do not mature into eggs They are polar bodies n which eventually degrade Oogonium Mitosis Additional oogonia Primary oocyte First meiotic division First plarhody I It V This second 39 meiotic division Secondawoocyte occurs in some 5 ecies onl Second quot 3quot meiotic division gt gt 35 Qatar9quot 39 a w V polarbody zygote Eggs are large mainly because they contain the nutrients required for the embryo s early development An egg cell contains a yolk a fat and protein rich cytoplasm that is loaded into egg cells as they mature Just outside the plasma membrane of eggs a brous mat like sheet of glycoproteins called the vitelline envelope forms and surrounds the egg ln eggs of mammals it is unusually thick and is called the zona pellucida A protective layer called the corona radiata surrounds human oocytes Fertilization is the joining of a sperm and an egg to form a diploid zygote 2n When individuals release their gametes into their environment external fertilization occurs When males deposit sperm into the reproductive tracts of females internal fertilization occurs Lectures 35 36 amp 37 Genetics Ch 1415 Mendel s Experimental System Genetics is the branch of biology that focuses on the inheritance of traits any characteristic of an individual Heredity is the inheritance or transmission of traits from parents to offspring There were two prevalent hypotheses of inheritance at the time of Mendel 1 Blending Inheritance Parental traits blend such that their offspring have intermediate traits Mende s work contradicted this hypothesis 2 Inheritance of acquired characteristics Parental traits are modi ed then passed on to their offspring Mendel chose the garden pea as his model organism because it is easy to grow it has a short reproductive cycle it produces large numbers of seeds its matings are easy to control and its traits are easily recognizable Peas pollinate themselves through selffertilization Mendel used crosspollination to control mating Mendel worked with varieties that differed in seven easily recognizable traits seed shape seed color pod shape pod color ower color ower and pod position and stem length Mendel s pea population had two distinct phenotypes observable features for each of the seven traits Mendel began his work by obtaining individuals from pure lines individuals that produce offspring identical to themselves when they are selfpollinated or crossed to another pure line Hybrids are offspring from matings between true breeding parents that differ in one or more traits Mendel s Experiments With a Single Trait Mendel s rst experiments involved crossing pure lines that differed in just one trait The adults in the cross were the parental generation P1 The offspring were the F1 generation The traits did not blend together but instead one trait disappeared The one that disappeared reappeared in the F2 generation A mating between parents that each carry two different genetic determinants for the same trait is called a monohybrid cross The trait that was visible in the F1 hybrids is called dominant The traits that disappeared in the F1 generation and reappeared in the F2 generation are called recessive Mendel repeated these experiments and found that in a monohybrid cross the dominant trait was present in a 31 ratio in the F2 generation He performed a reciprocal cross to determine if gender in uenced inheritance This is when you switch the phenotypes between the father and mother in a subsequent cross Mendel proposed the particulate inheritance hypothesis suggesting that genes hereditary determinants maintain their integrity from generation to generation nstead of blending they act as discrete entities or particles He also proposed that each individual has two versions of each gene or alleles These were responsible for the variation in the traits The alleles found in an individual are called its genotype To explain the 31 ratio he developed the principle of segregation which stated that two members of each gene pair must separate into different gamete cells during the formation of eggs and sperm in the parents As a result each gamete contains on allele of each gene Individuals with two copies of the same allele RR or rr are homozygous Individuals with two different alleles for the same gene Rr are heterozygous Mendel s Experiments with Two Traits A mating between two individuals that are both heterozygous for two traits is a dihybrid cross Mendel tested two contrasting hypotheses 1 Independent assortment alleles of different genes are transmitted independently of each other 9331 ratio in F2 9 genotypes and 4 phenotypes If parent is RrYy gametes will be RY ry Ry rY CORRECT 2 Dependent assortment The transmission of one allele depends on the transmission of another 31 ratio in F2 4 genotypes and 2 phenotypes lf parent is RrYy gametes will be RY ry Mendel used a testcross when a parent that is homozygous recessive for a particular trait is mated with a parent that has the dominant phenotype but an unknown genotype You can determine the genotype this way IV The Chromosome Theory of Inheritance The chromosome theory of inheritance stated that chromosomes are composed of genes and that meiosis explains the principle of segregation and independent assortment The physical separation of alleles during anaphase l of meiosis l is responsible for the principle of segregation The genes for different traits assort independently of one another at metaphase of meiosis I because they are located on different nonhomologous chromosomes 0 Genes on the same chromosome will not assort independenUy Wild type is the most common phenotype for each trait whereas mutations are phenotypes that differ from the wild type X and Y chromosomes are referred to as sex chromosomes and all others are autosomes Sex chromosomes pair during meiosis l and segregate during meiosis ll resulting in gametes with either an X or Y chromosome The inheritance of genes on sex chromosomes is sex linked inheritance Xlinkage is a gene residing on the X chromosome 0 Color blindness is an example Ylinkage is a gene residing on the Y chromosome 0 Most Ylinked genes help determine sex According to the hypothesis of Xlinkage a female fruit y has two copies of the gene that speci es eye color because she has two X chromosomes One of these chromosomes came from her female parent the other from her male parent A male in contrast only has one copy of the eye coor gene because he has only one X chromosome inherited from his mother Genes on nonsex chromosomes are said to show autosomal inheritance The discovery of XIinked inheritance convinced most biologists that the chromosome theory of inheritance was correct V Extending Mendel s Rules Linkage is the tendency of particular alleles of different genes to be inherited together Linked genes should violate the principle of independent assortment To determine whether linked traits always stay linked Morgan performed crosses between XWYXWy females mated with XWYY males He recorded only results from male offspring to gure out which XIinked alleles were present on the chromosomes produced during meiosis in the mother Since there is a single X chromosome in the male offspring the phenotype associated with any XIinked aee dominant or recessive is expressed Most males carried an X chromosome with one of the two combinations of alleles found in the chromosomes of their mothers XWY or XWV A small percentage of males had new combinations of phenotypes and genotypes These are recombinant This is the combination of alleles on their X chromosome was different from the combinations of alleles present in the parental generation Morgan proposed that gametes with recombinant genotypes were generated when crossing over occurred during prophase of meiosis in females Linked genes are inherited together unless crossing over occurs When crossing over takes place genetic recombination occurs Genes are more likely to cross over when they are far apart from each other than when they are close together because they have to form a chiasmata VI Frequency of crossing over can be used to create a genetic map a diagram showing the relative positions of genes along a particular chromosome The existence of more than two alleles of the same gene is known as multiple allelism When more than two distinct phenotypes are present in a population due to multiple aeism the trait is called polymorphic A heterozygous organism that displays the phenotype of both alleles for a single gene is said to display codominance Neither allele is dominant or recessive to the other Human blood types are an example of multiple aeism and codominance An AB individual expresses both the A and B phenotypes Incomplete dominance is when heterozygotes have an intermediate phenotype red white pink A pleiotropic gene is a single gene that controls more than one trait The combined effect of genes and environment is referred to as genebyenvironment interaction The human genetic disease phenylketonuria PKU is an example Untreated this disease causes phenylalanine to accumulate in the body of affected individuals The expression of many genes depending on the presence or absence of other genes is called genebygene interactions The phenotype produced by an allele depends on the action of alleles of other genes Mendel worked with discrete traits characteristics that are qualitatively different No intermediate phenotypes exist Traits that are not discrete but fall into a continuum are quantitative traits If many genes each contribute a small amount to the value of a quantitative trait then a normal distribution results for the population as a whole In polygenic inheritance each gene adds a small amount to the value of the phenotype Applying Mendel s Rules to Human Inheritance Pedigrees are family trees used to analyze human crosses that already exist They can be used to determine the mode of transmission of a trait that shows discrete variation When a phenotype is due to an autosomal recessive allele the individuals with the trait must be homozygous Unaffected parents of an affected individual are likely to be heterozygous carriers for the trait Example is sickle cell disease Characteristics 0 Males and females are equally likely to be affected 0 Affected offspring often have unaffected parents 0 Unaffected parents of affected offspring are heterozygous carriers 0 Affected offspring are homozygous o If both parents are heterozygous about 14 of the offspring will be affected 0 Trait often skips generations Autosomal dominant traits are expressed in any individual with at least one dominant allele Individuals homozygous or heterozygous for the trait will display the dominant phenotype Huntingdon s disease is an example Characteristics 0 Males and females are equally likely to be affected 0 Affected offspring have at least one affected parent 0 Affected offspring are heterozygous if only one parent is affected 0 Unaffected offspring are homozygous recessive o If one parent is heterozygous about 12 of the offspring will be affected 0 Trait does not skip generations If males are more likely to have the trait it is usually X linked Redgreen color blindness is an example of an Xlinked recessive trait Characteristics 0 Males are affected more frequently than females 0 Trait is never passed from father to son 0 Affected sons are usually born to carrier mothers 0 About 12 of the sons of a carrier mother will be affected 0 All daughters of affected males and unaffected non carrier females are carriers 0 Trait often skips generations Hypophosphatemia is an example of an Xlinked dominant trait Characteristics 0 Males and females are equally likely to be affected A daughters of an affected father are affected but no sons Affected sons always have affected mothers About 12 of the offspring of an affected mother will be affected Affected daughters can have an affected mother or father Trait doesn t skip generations


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