3Terms to Know Probability True-breeding Hybrid Segregation Traits GenesHomozygousHeterozygousPhenotypeGenotypeDominantRecessive
4Genes Chemical factors that determine traits (units of information) Analogy: Genes are like a combination of ingredients in a recipe. They code for a specific food.Passed from parents to offspringEach has a specific location (locus) on a chromosome
5AllelesDifferent forms of a gene (back to analogy…replacing jiffy p.b. with skippy p.b.)Dominant allele (Uppercase letter) overrules a recessive allele (lowercase letter) that it is paired with
6Allele Combinations Homozygous =purebred Heterozygous =hybrid having two identical alleles at a locusAA (dominant expressed) or aa (recessive expressed)Heterozygous =hybridhaving two different alleles at a locusAa (dominant expressed)
7Genotype & PhenotypeGenotype refers to particular genes an individual carriesPhenotype refers to an individual’s observable traitsCannot always determine genotype by observing phenotype
8Tracking Generations Parental generation P mates to produce First-generation offspring F1mate to produceSecond-generation offspring F2
9Earlobe VariationWhether a person is born with attached or detached earlobes depends on a single geneGene has two molecular forms (alleles)
11Earlobe VariationYou inherited one allele for this gene from each parentDominant allele specifies detached earlobes (E)Recessive allele specifies attached earlobes (e)
12Dominant & Recessive Alleles If you have attached earlobes, you inherited two copies of the recessive alleleIf you have detached earlobes, you may have either one or two copies of the dominant allele
13Early Ideas About Heredity People knew that sperm and eggs transmitted information about traitsBlending theoryProblem:Would expect variation to disappearVariation in traits persists
14Gregor Mendel Strong background in plant breeding and mathematics Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring
15Mendel was born in1822Austrian monkStudied at the Univ. of ViennaTeacher (High School)
16Figure 24–5 The Structure of a Flower Section 24-1FilamentAntherStigmaStyleOvaryCarpelPetalSepalOvuleStamen
17The Garden Pea Plant Self-pollinating True breeding (different alleles not normally introduced)Can be experimentally cross-pollinated
20Dominant trait is expressed FMDominant trait is expressedRecessive appears
21Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants Seed ShapeSeed ColorSeed CoatColorPodShapePod ColorFlower PositionPlant HeightRoundYellowGraySmoothGreenAxialTallWrinkledGreenWhiteConstrictedYellowTerminalShortRoundYellowGraySmoothGreenAxialTall
22F1 Results of Mendel’s Dihybrid Crosses All plants displayed the dominant form of both traitsWe now know:All plants inherited one allele for each trait from each parentAll plants were heterozygous (AaBb)
23Principle of Dominance Some alleles are dominant and others are recessive.
24Mendel wanted to know if the recessive alleles disappeared or are they still in the f1,just hidden.
25Principles of Dominance P GenerationF1 GenerationF2 GenerationTallShortTallTallTallTallTallShort
26Principles of Dominance P GenerationF1 GenerationF2 GenerationTallShortTallTallTallTallTallShort
27Principles of Dominance P GenerationF1 GenerationF2 GenerationTallShortTallTallTallTallTallShort
28Mendel’s Theory of Segregation An individual inherits a unit of information (allele) about a trait from each parentDuring gamete formation, the alleles segregate from each other
29Independent Assortment Mendel concluded that the two “units” for the first trait were to be assorted into gametes independently of the two “units” for the other traitMembers of each pair of homologous chromosomes are sorted into gametes at random during meiosis
30Independent Assortment Metaphase IORAAaaAAaaBBbbbbBBMetaphase II:AAaaAAaaBBbbbbBBGametes:BBbbbbBBAAaaAAaa1/4 AB1/4 ab1/4 Ab1/4 aB
51Dominance Relations Complete dominance Incomplete dominance Heterozygote phenotype is somewhere between that of two homozyotesCodominanceNon-identical alleles specify two phenotypes that are both expressed in heterozygotes
52Flower Color in Snapdragons: Incomplete Dominance Red-flowered plant X White-flowered plantPink-flowered F1 plants(homozygote)(homozygote)(heterozygotes)
53Flower Color in Snapdragons: Incomplete Dominance Red flowers - two alleles allow them to make a red pigmentWhite flowers - two mutant alleles; can’t make red pigmentPink flowers have one normal and one mutant allele; make a smaller amount of red pigment
54Figure 11-11 Incomplete Dominance in Four O’Clock Flowers
55Figure 11-11 Incomplete Dominance in Four O’Clock Flowers
56Flower Color in Snapdragons: Incomplete Dominance Pink-flowered plant X Pink-flowered plantWhite-, pink-, and red-flowered plantsin a 1:2:1 ratio(heterozygote)(heterozygote)
57Incomplete Dominance Neither allele is dominant over the other Combination of red and white flowers
61Genetics of Sickle-Cell Anemia Two alleles1) HbAEncodes normal beta hemoglobin chain2) HbSMutant allele encodes defective chainHbS homozygotes produce only the defective hemoglobin; suffer from sickle-cell anemia
62Pleiotrophic Effects of HbS/HbS At low oxygen levels, cells with only HbS hemoglobin “sickle” and stick togetherThis impedes oxygen delivery and blood flowOver time, it causes damage throughout the body
63Blood Typing Karl Landsteiner 1897 Worked at the Univ. of Vienna, Vienna Austria (Sound familiar?)Wanted to find out which red blood cells would clot
64First found two different groups, A and B Third group would not clot when exposed to A or B What do you think this was?What about the forth group?
65Genetics of ABO Blood Types: Three Alleles Gene that controls ABO type codes for enzyme that dictates structure of a glycolipid on blood cellsTwo alleles (IA and IB) are codominant when pairedThird allele (i) is recessive to others
66ABO Blood Type: Glycolipids on Red Cells Type A - Glycolipid A on cell surfaceType B - Glycolipid B on cell surfaceType AB - Both glyocolipids A & BType O - Neither glyocolipid A nor B
67ABO Blood Type: Allele Combinations Type A - IAIA or IAiType B - IBIB or IBiType AB - IAIBType O - ii
68ABO and TransfusionsRecipient’s immune system will attack blood cells that have an unfamiliar glycolipid on surfaceType O is universal donor because it has neither type A nor type B glycolipid
69Codominance and Multiple Alleles - AB or NOT AB Codominance - both alleles are dominantIA and IBMultiple Alleles - genes have more than two allelesIA, IB, Ia
70Figure 14-4 Blood Groups Safe Transfusions Phenotype Antigen on (Blood TypeAntigen onRed Blood CellGenotypeToFrom
79Cystic Fibrosis - Finding Cures is Hard Sex-Linked DisorderCystic Fibrosis - Finding Cures is Hard
80Hairy Pinna - long hair on ears Male Pattern Baldness (X chromosome)Hairy Pinna - long hair on ears
81Recessive Disorder Figure 14-8 The Cause of Cystic Fibrosis Chromosome # 7CFTR geneThe most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein.Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane.The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus.
82AlbinismPhenotype results when pathway for melanin production is completely blockedGenotype - Homozygous recessive at the gene locus that codes for tyrosinase, an enzyme in the melanin-synthesizing pathway
87Tracing Genes Through Families - Human Pedigrees FemalePartnerMaleBrothers and Sisters
88Figure 14-3 A Pedigree A circle represents a female. A square represents a male.A horizontal line connecting a male and female represents a marriage.A vertical line and a bracket connect the parents to their children.A half-shaded circle or square indicates that a person is a carrier of the trait.A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait.A completely shaded circle or square indicates that a person expresses the trait.
90Ability to roll the tongue in the Senator Family Tongue Roller - dominant, Non-Tongue Roller - recessiveWhite = tongue roller, Purple = non-rollerWhat are the genotypes of everyone? R = roller, r = non roller
91George, Sam, Ann, Michael, Daniel and Alan are Rr Arlene, Tom, Wilma, and Carla are rrSandra, Tina and Christopher are either RR or Rr
941. First, let’s take a look at Queen Victoria’s son Leopold’s family 1. First, let’s take a look at Queen Victoria’s son Leopold’s family. His daughter, Alice of Athlone, had one hemophilic son (Rupert) and two other children—a boy and a girl—whose status is unknown. a) What is the probability that her other son was hemophilic? b) What is the probability that her daughter was a carrier? Hemophilic? c) What is the probability that both children were normal?
952. Now for the Spanish connection: Victoria’s youngest child, Beatrice, gave birth to one daughter, one normal son, and two hemophilic sons. Looking at the pedigree of the royal family, identify which of Beatrice’s children received the hemophilic gene; why can you make this conclusion? Notice that Beatrice’s daughter, Eugenie, married King Alfonso XIII of Spain and had six children, one of whom was the father of Juan Carlos, the current King of Spain. Would you predict that Juan Carlos was normal, a carrier, or a hemophilic?
963. Alexis did not die from hemophilia 3. Alexis did not die from hemophilia. At the age of fourteen he was executed with the rest of the family. His four oldest sisters were also young and didn’t have children, so we don’t know whether any of them was a carrier. But we can make an estimate. a) What are the probabilities that all four of the girls were carriers of the allele hemophilia? b) Supposing Alexis had lived and married a normal woman, what are the chances that his daughter would be a hemophiliac? c) What are the chances his daughters would be carriers? d) What are the chances that his sons would be hemophiliacs?
97Homologous chromosomes fail to separate NondisjunctionHomologous chromosomes fail to separateMeiosis I:NondisjunctionMeiosis II
98Homologous chromosomes fail to separate NondisjunctionHomologous chromosomes fail to separateMeiosis I:NondisjunctionMeiosis II
99Homologous chromosomes fail to separate NondisjunctionHomologous chromosomes fail to separateMeiosis I:NondisjunctionMeiosis II
100Epistasis Interaction between the products of gene pairs Common among genes for hair color in mammals
101Genetics of Coat Color in Labrador Retrievers Two genes involved- One gene influences melanin productionTwo alleles - B (black) is dominant over b (brown)- Other gene influences melanin depositionTwo alleles - E promotes pigment deposition and is dominant over e
102Allele Combinations and Coat Color Black coat - Must have at least one dominant allele at both lociBBEE, BbEe, BBEe, or BbEEBrown coat - bbEE, bbEeYellow coat - Bbee, BbEE, bbee
103Alleles at two loci (R and P) interact Comb Shape in PoultryAlleles at two loci (R and P) interactWalnut comb - RRPP, RRPp, RrPP, RrPpRose comb - RRpp, RrppPea comb - rrPP, rrPpSingle comb - rrpp
104Campodactyly: Unexpected Phenotypes Effect of allele varies:Bent fingers on both handsBent fingers on one handNo effectMany factors affect gene expression
105Continuous VariationA more or less continuous range of small differences in a given trait among individualsThe greater the number of genes and environmental factors that affect a trait, the more continuous the variation in versions of that trait
106Human Variation Some human traits occur as a few discrete types Attached or detached earlobesMany genetic disordersOther traits show continuous variationHeightWeightEye color
107Temperature Effects on Phenotype Himalayan rabbits are Homozygous for an allele that specifies a heat-sensitive version of an enzyme in melanin-producing pathwayMelanin is produced in cooler areas of body
108Environmental Effects on Plant Phenotype Hydrangea macrophyllaAction of gene responsible for floral color is influenced by soil acidityFlower color ranges from pink to blue