1. The Chromosome Theory of Inheritance http://www.biology.usu.edu/courses/biol3060- wolf/power%20points/chapt04b_lecture.ppt

2. Outline of Chromosome Theory of Inheritance Observations and experiments determined the hereditary material in the nucleus on the chromosomes Observations and experiments determined the hereditary material in the nucleus on the chromosomes Mitosis ensures that every cell in an organism carries same set of chromosomes Mitosis ensures that every cell in an organism carries same set of chromosomes Meiosis distributes one member of each chromosome pair to gamete cells Meiosis distributes one member of each chromosome pair to gamete cells Validation of the chromosome theory of inheritance Validation of the chromosome theory of inheritance

3. Evidence that Genes Reside in the Nucleus 1667 – Anton van Leeuwenhoek 1667 – Anton van Leeuwenhoek Semen contains spermatozoa (sperm animals) Semen contains spermatozoa (sperm animals) Hypothesized that sperm enter egg to achieve fertilization Hypothesized that sperm enter egg to achieve fertilization 1854-1874 – confirmation of fertilization through union of eggs and sperm 1854-1874 – confirmation of fertilization through union of eggs and sperm Recorded frog and sea urchin fertilization using microscopy and time-lapse drawings and micrographs Recorded frog and sea urchin fertilization using microscopy and time-lapse drawings and micrographs

4. Evidence that Genes Reside in Chromosomes 1880s – innovations in microscopy and staining techniques identified thread-like structures 1880s – innovations in microscopy and staining techniques identified thread-like structures Follow movement of chromosomes during cell division Follow movement of chromosomes during cell division Mitosis – two daughter cells contained same number of chromosomes as parent cell (somatic cells) Mitosis – two daughter cells contained same number of chromosomes as parent cell (somatic cells) Meiosis – daughter cells contained half the number of chromosomes as the parents (sperm and eggs) Meiosis – daughter cells contained half the number of chromosomes as the parents (sperm and eggs)

5. One Chromosome Pair Determines an Individuals Sex Walter Sutton – Studied great lubber grasshopper Walter Sutton – Studied great lubber grasshopper Parent cells contained 22 chromosomes plus an X and a Y chromosome Parent cells contained 22 chromosomes plus an X and a Y chromosome Daughter cells contained 11 chromosomes and X or Y in equal numbers Daughter cells contained 11 chromosomes and X or Y in equal numbers

6. After fertilization After fertilization Cells with XX were females Cells with XX were females Cells with XY were males Cells with XY were males Great lubber grasshopper (Brachystola magna) Fig. 4.2

7. Sex chromosome Sex chromosome Provide basis for sex determination Provide basis for sex determination One sex has matching pair One sex has matching pair Other sex has one of each type of chromosome Other sex has one of each type of chromosome Photomicrograph of human X and Y chromosome Fig. 4.3a

8. Sex determination in humans Sex determination in humans Children receive only an X chromosome from mother but X or Y from father Children receive only an X chromosome from mother but X or Y from father Fig. 4.3b

9. The number and shape of chromosomes vary from species to species 4623Humans 7839Dogs 1260630Ophioglossum reticulatum (fern) 2211Giant sequoia trees 2814Macaroni wheat 147Peas 126Drosophila virilus 105Drosophila obscura 84Drosophila melanogaster 2nn Organism

10. Karyotypes can be produced by cutting micrograph images of stained chromosomes and arranging them in matched pairs Human male karyotype Fig 4.6

11. Autosomes – pairs of nonsex chromosomes Sex chromosomes and autosomes are arranged in homologous pairs Note 22 pairs of autosomes and 1 pair of sex chromosomes

12. There is variation between species in how chromosomes determine an individuals sex __________________________________________________ Chromosome Females MalesOrganism __________________________________________________ XX-XY XX XY Mammals, Drosophila XX-XO XX XO Grasshoppers ZZ-ZW ZW ZZ Fish, Birds, Moths __________________________________________________

13. DiesNormal or nearly normal male Normal male Turner female (sterile); webbed neck Kleinfelter male (sterile); tall, thin Normal female Nearly normal female Humans DiesNormal male Sterile male Normal female Dies Drosophila OYXYYXYXOXXYXXXXX Complement of sex chromosomes Humans – presence of Y determines sex Drosophila – ratio of autosomes to X chromosomes

14. Meiosis contributes to genetic diversity in two ways Independent assortment of nonhomologous chromosomes creates different combinations of alleles among chromosomes Independent assortment of nonhomologous chromosomes creates different combinations of alleles among chromosomes Crossing-over between homologous chromosomes creates different combinations of alleles within each chromosome Crossing-over between homologous chromosomes creates different combinations of alleles within each chromosome

15. Specific traits are transmitted with specific chromosomes A test of the chromosome theory. A test of the chromosome theory. If genes are on specific chromosomes, then traits determined by the gene should be transmitted with the chromosome If genes are on specific chromosomes, then traits determined by the gene should be transmitted with the chromosome T.H. Morgans experiments demonstrating sex- linked inheritance of a gene determining eye-color demonstrate the transmission of traits with chromosomes T.H. Morgans experiments demonstrating sex- linked inheritance of a gene determining eye-color demonstrate the transmission of traits with chromosomes 1910 – T.H. Morgan discovered a white – eyed male Drosophila melanogaster among his stocks 1910 – T.H. Morgan discovered a white – eyed male Drosophila melanogaster among his stocks

16. Criss-cross inheritance of the white gene demonstrates X-linkage Fig. 4.20

17. X and Y linked traits in humans are identified by pedigree analysis X-linked traits exhibit five characteristics seen in pedigrees X-linked traits exhibit five characteristics seen in pedigrees Trait appears in more males than females Trait appears in more males than females Mutation and trait never pass from father to son Mutation and trait never pass from father to son Affected male does pass X-linked mutation to all daughters, who are heterozygous carriers Affected male does pass X-linked mutation to all daughters, who are heterozygous carriers Trait often seems to skip a generation Trait often seems to skip a generation Trait only appears in successive generations if sister of an affected male is a carrier. If so, one half of her sons will show trait Trait only appears in successive generations if sister of an affected male is a carrier. If so, one half of her sons will show trait

18. Example of sex-linked recessive trait in human pedigree – hemophilia

19. Example of sex-linked dominant trait in human pedigree – hypophosphatemia Fig. 4.23 b