Presentation on theme: "AP Biology Chapter 15 The Chromosome Theory of Inheritance"— Presentation transcript:
1 AP Biology Chapter 15 The Chromosome Theory of Inheritance Genes and ChromosomesAP BiologyChapter 15The Chromosome Theory of Inheritance
2 Genes are Located on Chromosomes Mendel’s “factors” are now known to be genes—segments of chromosomes.Where the chromosomes go during Meiosis determines which traits end up in each of the gametes.
3 The Chromosome Theory of Inheritance First described by Walter S. Sutton in 1902:Genes have specific loci (positions) along chromosomesIt is the chromosomes that undergo segregation and independent assortment
4 The Chromosomal Basis of Mendel’s Laws: Yellow-roundseeds (YYRR)Green-wrinkledseeds ( yyrr)P GenerationyYrRRrYyMeiosisFertilizationyrRYFigure 15.2 The chromosomal basis of Mendel’s lawsGametesAll F1 plants produceyellow-round seeds (YyRr)
5 0.5 mm All F1 plants produce yellow-round seeds (YyRr) F1 Generation LAW OF SEGREGATIONThe two alleles for each geneseparate during gameteformation.MeiosisLAW OF INDEPENDENTASSORTMENT Alleles of geneson nonhomologouschromosomes assortindependently during gameteformation.RrrRMetaphase IYyYy11RrrRAnaphase IYyYyRrMetaphase IIFigure 15.2 The chromosomal basis of Mendel’s lawsrR22YyYyyYYYyYyyGametesRRrrrrRR14YR14yr14Yr14yR33
6 Fertilization recombines the R and r alleles at random Fertilization recombines the R and r alleles at random. On a different chromosome, fertilization recombines theY and y alleles also. YyRr X YyRr produces 9:3:3:1 ratio.F2 GenerationAn F1 F1 cross-fertilization339: 3: 3: 1Figure 15.2 The chromosomal basis of Mendel’s lawsSo, Mendel’s ratios can be explained by examining the behavior of the chromosomes during meiosis.
7 Morgan’s Experimental Evidence: Scientific Inquiry The first solid evidence associating a specific gene with a specific chromosome came from Thomas Hunt Morgan, an embryologist.Morgan’s experiments with fruit flies provided convincing evidence that chromosomes are the location of Mendel’s heritable factors.
8 Morgan’s Choice of Experimental Organism Thomas Hunt Morgan chose Drosophila melanogaster, a common insect that feeds on the fungi growing on fruit. Why?They are prolific breeders (a single mating can produce hundreds of offspring)They can be bred everytwo weeksIt has only 4 pairs ofchromosomesThere are many typesof easily identified mutantswhich differ from the normal(wild) type.
9 Wild Type Fruit Flies vs. Mutants When Thomas Hunt Morgan studied fruit flies, he was looking for naturally occurring variants. After years of study, he finally found one male fruit fly with white eyes instead of the usual red.The allele for the mutant trait is written as a lower case letter (ex: white eyes is w). The wild-type fly (normal phenotype) is shown with the same letter with a superscript+: w+
10 Correlating behavior of an allele with behavior of the chromosome EXPERIMENTPGenerationF1All offspringhad red eyesGenerationFigure 15.4 In a cross between a wild-type female fruit fly and a mutant white-eyed male, what color eyes will the F1 and F2 offspring have?In one experiment, Morgan mated a white-eyed male with a red-eyed female.All of the F1 offspring had red eyes. What does this tell us about the red eye trait?
11 Fig. 15-4bF2 Results:RESULTSF2GenerationWhen Morgan bred the F1 flies to each other, he observed the classical 3:1 phenotypic ratio in the F2 offspring.However, surprisingly, the white-eyed trait showed up only in the males! Somehow, the fly’s eye color is related to its sex.Figure 15.4 In a cross between a wild-type female fruit fly and a mutant white-eyed male, what color eyes will the F1 and F2 offspring have?
12 CONCLUSION + P X X Generation X Y + Sperm Eggs + + F1 + Generation + wwXXGenerationXY+wwSpermEggs++F1ww+Generationww+wFigure 15.4 In a cross between a wild-type female fruit fly and a mutant white-eyed male, what color eyes will the F1 and F2 offspring have?SpermEggs++ww+F2wGenerationwww+w
13 The Chromosomal Basis of Sex In humans and other mammals, there are two varieties of sex chromosomes: a larger X chromosome and a smaller Y chromosomeOnly the ends of the Y chromosome have regions that are homologous with the X chromosomeX and Y chromosomes →The SRY gene on the Y chromosome codes for the development of the testes.
14 (a) The X-Y system 44 + XY 44 + XX Parents 22 + X 22 + X 22 + Y or + In mammals, the sex of an offspring depends on whether the sperm cell contains an X chromosome or a Y.SpermEggFigure 15.6 Some chromosomal systems of sex determination44 +XX44 +XYorZygotes (offspring)(a) The X-Y system
15 Fig. 15-6b22 +XX22 +X(b) The X-0 systemFigure 15.6 Some chromosomal systems of sex determinationIn grasshoppers, cockroaches, and some other insects, there is only one type of sex chromosome, the X. Females are XX, males have only one sex chromosome (XO). Sex of the offspring is determined by whether the sperm cell contains an X chromosome or no sex chromosome.
16 (c) The Z-W system 76 + ZW 76 + ZZ Fig. 15-6c76 +ZW76 +ZZFigure 15.6 Some chromosomal systems of sex determination(c) The Z-W systemIn birds, some fishes, and some insects, the sex chromosomes present in the egg (not the sperm) determine the sex of offspring. The sex chromosomes are designated Z and W. Females are ZW and males are ZZ.
17 (d) The haplo-diploid system Fig. 15-6d32(Diploid)16(Haploid)Figure 15.6 Some chromosomal systems of sex determination(d) The haplo-diploid systemThere are no sex chromosomes in most species of bees and ants. Females develop from fertilized eggs and are thus diploid. Males develop from unfertilized eggs and are haploid; they have no fathers.
18 Inheritance of Sex-Linked Genes The sex chromosomes have genes for many characters unrelated to sexA gene located on either sex chromosome is called a sex-linked geneIn humans, sex-linked usually refers to a gene on the larger X chromosome
19 Inheritance Patterns of Sex Chromosomes. Sex-linked genes follow specific patterns of inheritanceFor a recessive sex-linked trait to be expressedA female needs two copies of the alleleA male needs only one copy of the alleleSex-linked recessive disordersare much more common inmales than in females
20 The Transmission of Sex-linked recessive traits. Fig. 15-7The Transmission of Sex-linked recessive traits.XNXNXnYXNXnXNYXNXnXnYSpermXnYSpermXNYSpermXnYEggsXNXNXnXNYEggsXNXNXNXNYEggsXNXNXnXNYXNXNXnXNYXnXnXNXnYXnXnXnXnYFigure 15.7 The transmission of sex-linked recessive traits(a)(b)(c)If a carrier mates with a color-blind male, there is a 50% chance their child will be color-blind.A color-blind father will transmit the mutant allele to all daughters but not to sons. Daughters are carriers.If a carrier mates with a male who has normal color vision, there is a 50% chance the son will be color-blind.
22 Barr Bodies: the inactive X in each cell of a female If a female is heterozygous for a particular gene located on the X chromosome, she will be a mosaic for that character
23 The tortoiseshell gene is on the X chromosome in cats. X chromosomesAllele fororange furEarly embryo:Allele forblack furCell division andX chromosomeinactivationTwo cellpopulationsin adult cat:Active XInactive XActive XThe tortoiseshell gene is on the X chromosome in cats.The tortoiseshell color requires the presence of two alleles: one orange and one black. These are located on the X chromosome.Black furOrange furFigure 15.8 X inactivation and the tortoiseshell catIf a female (XX) is heterozygous, the orange and black patches are present in populations of cells with that activated gene.
24 Linked GenesGenes located near each other on the same chromosome tend to be inherited together.These are called linked genes.These are not to be confused with sex-linked traits (traits that come from the sex chromosomes)
26 Linked GenesIn the fruit fly Drosophila melanogaster, flies reared in the laboratory occasionally exhibit mutations in their genes.Two such mutations, affecting body color and wing structure are linked. Morgan did experiments studying these two traits.Grey body and normal wings are dominant traits.Black body and vestigial wings are recessive
27 b+ vg+ b vg Parents in testcross b vg b vg b+ vg+ b vg Most or Fig. 15-UN1Homozygous for black body, vestigial wingsHeterozygous for grey body, normal wingsXb+ vg+b vgParentsin testcrossb vgb vgb+ vg+b vgMostoffspringorb vgb vgGrey body, normal wingsBlack body, vestigical wings
28 EXPERIMENT P Generation (homozygous) b+ b+ vg+ vg+ b b vg vg Wild type(gray body,normal wings)Double mutant(black body,vestigial wings)b+ b+ vg+ vg+b b vg vgFigure 15.9 How does linkage between two genes affect inheritance of characters?
29 EXPERIMENT Fig. 15-9-2 P Generation (homozygous) b+ b+ vg+ vg+ Wild type(gray body,normal wings)Double mutant(black body,vestigial wings)b+ b+ vg+ vg+b b vg vgF1 dihybrid(wild type)Double mutantTESTCROSSb+ b vg+ vgb b vg vgFigure 15.9 How does linkage between two genes affect inheritance of characters?
30 EXPERIMENT P Generation (homozygous) b+ b+ vg+ vg+ b b vg vg Wild type(gray body,normal wings)Double mutant(black body,vestigial wings)b+ b+ vg+ vg+b b vg vgF1 dihybrid(wild type)Double mutantTESTCROSSb+ b vg+ vgb b vg vgTestcrossoffspringEggsb+ vg+b vgb+ vgb vg+Wild type(gray-normal)Black-vestigialGray-vestigialBlack-normalb vgFigure 15.9 How does linkage between two genes affect inheritance of characters?Spermb+ b vg+ vgb b vg vgb+ b vg vgb b vg+ vg
31 EXPERIMENT RESULTS P Generation (homozygous) b+ b+ vg+ vg+ b b vg vg Wild type(gray body,normal wings)Double mutant(black body,vestigial wings)b+ b+ vg+ vg+b b vg vgF1 dihybrid(wild type)Double mutantTESTCROSSb+ b vg+ vgb b vg vgTestcrossoffspringEggsb+ vg+b vgb+ vgb vg+Wild type(gray-normal)Black-vestigialGray-vestigialBlack-normalb vgFigure 15.9 How does linkage between two genes affect inheritance of characters?Spermb+ b vg+ vgb b vg vgb+ b vg vgb b vg+ vgPREDICTED RATIOSIf genes are located on different chromosomes:1:1:1:1If genes are located on the same chromosome andparental alleles are always inherited together:1:1::RESULTS965:944:206:185
35 Recombination of Unlinked Genes When traits appear that are different from either one of the parents, it is due to independent assortment when genes are not on the same chromosome.Parental types: resemble the parentsRecombinants: contain new combinations of genesIf genes are located on different chromosomes, there will be a 50% recombination rate.RecombinantsParental types
36 Recombinants YR yr Yr yR yr YyRr yyrr Yyrr yyRr Gametes from yellow-roundheterozygous parent (YyRr)YRyrYryRGametes from green-wrinkled homozygousrecessive parent ( yyrr)yrYyRryyrrYyrryyRrParental-typeoffspringRecombinantoffspring
37 Recombinants from Linked Genes Recombinations in traits that are located on the same chromosome (linked genes) are due to crossing over.
39 Mapping the distance between two genes: Alfred Sturtevant, one of Morgan’s students, constructed a genetic map, an ordered list of the genetic loci along a particular chromosomeSturtevant predicted that the farther apart two genes are, the higher the probability that a crossover will occur between them and therefore the higher the recombination frequency
41 Genetic Linkage MapsA linkage map is a genetic map of a chromosome based on recombination frequenciesDistances between genes can be expressed as map units; one map unit, or centimorgan, represents a 1% recombination frequencyMap units indicate relative distance and order, not preciselocations of genes
42 A linkage map from Drosophila: RESULTSRecombinationfrequencies9%9.5%Chromosome17%Figure Constructing a linkage mapbcnvgGenes that are far apart on a chromosome can have recombination frequencies close to 50%.(These behave almost the same as if they were on difference chromosomes)
43 How to figure out recombination frequencies: Determine which traits are like the original parents (parental traits). Determine which traits are new combinations of the genes (these are the recombinants)Figure out the total number of recombinant offspring and divide by the total number of offspring X 100 = Recombination %What is the recombination frequencies of the b and vg genes?
44 Now You Try:A wild-type fruit fly heterozygous for gray body color and normal wings, b+b vg+vg, is mated with a black fly with vestigial wings bbvgvg. The offspring have the following phenotypic distribution:Wild-type (gray, normal wings): 778Black-vestigial: 785Black-normal wings: 158Gray-vestigial: 162What is the recombination frequency between these genes for body color and wing size?
45 Answer Number recombinants = 320 Total offspring = 1883 Recombinant frequency = 320/1883 X 100 =17%
46 Now You Try:Determine the sequence of genes along a chromosome based on the following recombination frequencies:A—B , 8 map unitsA—C, 28 map unitsA—D, 25 map unitsB—C, 20 map unitsB—D, 33 map units
48 Chromosome Alterations/Mutations Cause Genetic Disorders Large-scale chromosomal alterations often lead to spontaneous abortions (miscarriages) or cause a variety of developmental disordersChildren with Down’s Syndrome/ Trisomy 21
49 Abnormal Chromosome Number In nondisjunction, pairs of homologous chromosomes do not separate normally during meiosisAs a result, one gamete receives two of the same type of chromosome, and another gamete receives no copyOffspring withthis conditionis calledaneuploidy
50 Meiosis I (a) Nondisjunction of homologous FigMeiosis INondisjunctionFigure Meiotic nondisjunctionFor the Cell Biology Video Nondisjunction in Mitosis, go to Animation and Video Files.(a) Nondisjunction of homologouschromosomes in meiosis I(b) Nondisjunction of sisterchromatids in meiosis II
51 Meiosis I Meiosis II (a) Nondisjunction of homologous FigMeiosis INondisjunctionMeiosis IINondisjunctionFigure Meiotic nondisjunction(a) Nondisjunction of homologouschromosomes in meiosis I(b) Nondisjunction of sisterchromatids in meiosis II
52 Meiosis I Meiosis II Gametes (a) Nondisjunction of homologous FigMeiosis INondisjunctionMeiosis IINondisjunctionGametesFigure Meiotic nondisjunctionn + 1n + 1n – 1n – 1n + 1n – 1nnNumber of chromosomes(a) Nondisjunction of homologouschromosomes in meiosis I(b) Nondisjunction of sisterchromatids in meiosis II
53 Monosomic, Trisomic Zygotes A monosomic zygote has only one copy of a particular chromosomeA trisomic zygote has three copies of a particular chromosomeTurner’s Syndrome Karyotype: XO (monosomic zygote)Down’s Syndrome Karyotype:Trisomy 21
54 PolyploidyPolyploidy is a condition in which an organism has more than two complete sets of chromosomesPolyploidy is common in plants, but not animals. In plants, it may result in hybrids that are more vigorous.Polyploidy can result when a 2N zygote fails to divide after replicating its chromosomes. This will produce a 4N embryo. (Note the hybrid vigor in the middle plant)
55 Alterations of Chromosome Structure Breakage of a chromosome can lead to four types of changes in chromosome structure:Deletion removes a chromosomal segmentDuplication repeats a segmentInversion reverses a segment within a chromosomeTranslocation moves a segment from one chromosome to anotherCri du chat results from a deletion of a portion of chromosome 5.
56 Reciprocal translocation A B C D E F G HA B C E F G HDeletion(a)A B C D E F G HA B C B C D E F G HDuplication(b)A B C D E F G HA D C B E F G H(c)InversionFigure Alterations of chromosome structureA B C D E F G HM N O C D E F G H(d)ReciprocaltranslocationM N O P Q RA B P Q R
57 Translocated chromosome 22 (Philadelphia chromosome) TranslocationReciprocaltranslocationNormal chromosome 9Translocated chromosome 9Translocated chromosome 22(Philadelphia chromosome)Normal chromosome 22Figure Translocation associated with chronic myelogenous leukemia (CML)The cancerous cells in nearly all CML (chromic myelogenous leukemia) patients contain an abnormally short chromosome 22, the so-called Philadelphia chromosome, and an abnormally long chromosome 9. These altered chromosomes result from translocation.