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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
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

slide4

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?

human y chromosome
Human Y chromosome
  • Yellow: pseuoautosomal regions
  • Red: genes with homologs on the X chromosome
  • Blue: genes without homologus on the X
genetically what determines gender in mammals
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.

dosage compensation
Dosage Compensation

Do males have half as much of the products of genes on the X as do females?

x inactivation
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

which x gets inactivated
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 _______

_________________.

slide12

In 64-cell embryos

Adult female mammals are ___________ for genes on the X chromosome.

genetic mosaics
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

x inactivation is different in marsupials
X inactivation is different in marsupials

kangaroos, wombats, bandicoots, opossums