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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Homework due 9:00 Thursday
Review Session Sunday 3:00 to 4:00 PM
124 Burrill Hall
Exam Tuesday 9:00 AM, in Lecture room
How do they segregate normally at Meiosis?
During what part of Meiosis do they pair and then segregate?
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.
Do males have half as much of the products of genes on the X as do females?
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
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 _______
Adult female mammals are ___________ for genes on the X chromosome.
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 colorGenetic Mosaics
kangaroos, wombats, bandicoots, opossums