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Announcements

Announcements. Homework due 9:00 Thursday only your first grade will count! Review Session Sunday 3:00 to 4:00 PM 124 Burrill Hall Exam Tuesday 9:00 AM, in Lecture room. Sex Chromosomes and Sex Determination. X and Y are clearly not homologous chromsomes.

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Announcements

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  1. Announcements Homework due 9:00 Thursday • only your first grade will count! Review Session Sunday 3:00 to 4:00 PM 124 Burrill Hall Exam Tuesday 9:00 AM, in Lecture room

  2. Sex Chromosomes and Sex Determination

  3. X and Y are clearly not homologous chromsomes. How do they segregate normally at Meiosis? During what part of Meiosis do they pair and then segregate?

  4. Human Y chromosome • Yellow: pseuoautosomal regions • Red: genes with homologs on the X chromosome • Blue: genes without homologus on the X

  5. Genetically, what determines gender in mammals? Presence of a single gene (SRY) that usually, but not always, occurs on the Y chromosome. If the Y chromosome is missing (this gene deleted) or has a non-functional mutation in the gene, an XY individual can be a perfectly normal female. If the SRY gene becomes translocated to another chromosome, an XX individual can be a phenotypically normal (but sterile) male.

  6. XX (+SRY) mice

  7. Dosage Compensation Do males have half as much of the products of genes on the X as do females?

  8. X Inactivation Barr Body: Inactive X Interphase: Chromomes can’t be stained, but a dark-staining body is visible in the nuclei of cells of female mammals

  9. Which X gets inactivated? Mary Lyon & Lianne Russell (1961) proposed that one or other of X becomes inactivated at a particular time in early development. Within each cell,which X becomes inactivated is ____________. As development proceeds, all cells arising by cell division after than time have _______ _________________.

  10. In 64-cell embryos Adult female mammals are ___________ for genes on the X chromosome.

  11. Calico cats are almost always ____________. One X chromosome carries the allele for black coat color The other X chromosome carries the allele for orange coat color In 64-cell embryos, one of each pair of X chromosomes and its genes are _____________ ________________. Daughter cells inherit active or inactive X chromosomes, creating a cat with patches of coat color Genetic Mosaics XOXo

  12. Tortoiseshell (calico) coat color allele allele

  13. Tortoiseshell (calico) coat color

  14. Tortoiseshell (calico) coat color

  15. Carbon Copy

  16. X inactivation is different in marsupials kangaroos, wombats, bandicoots, opossums

  17. Sex chromosome aberrations

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