1. The Y Chromosome *PAR - Pseudoautosomal region
*MSY – Male-specific region of Y
*SRY – Sex determining region
*TDF - Testis Determining Factor
Is the Y chromosome a “genetic wasteland”?

2. The Y Chromosome
SKALETSKY, et al. (2003) The male-specific region of the human Y chromosome is a mosaic of discrete sequence classes. Nature 423,

3. The X Chromosome and Dosage Compensation
*Do females produce twice as much of each gene product for X-linked genes?
Dosage compensation
*In mammals – X inactivation
*Barr and Bertram
*Susumo Ohno

4. The X Chromosome and Dosage Compensation
*If you can make one copy of X (in females) inactive, you can compensate for dosage
Indirect evidence:

5. X Inactivation *Lyon hypothesis Example:
Coat color in cats; G6PD in human fibroblasts

6. Review: X inactivation
Mechanism of inactivation:
XIC or X-inactivation center
Avner, P. and Heard, E. (2001); X-CHROMOSOME INACTIVATION: COUNTING, CHOICE AND INITIATION, Nature Reviews Genetics 2; 59-67

7. Sex determination in Drosophila:

8. Sex determination in Drosophila:

9. Temperature and sex determination: