1. MCDB 4650 Dosage Compensation

2. Which of the following is true of a worm that is homozygous mutant for xol-1 (lf)--one of the dosage compensation genes? a.XX embryos develop into male worms b.XO embryos develop into hermaphrodite worms c.XO embryos die due to lack of X chromosome gene products d.XX embryos die due to overproduction of X chromosome gene products

3. If they could survive, the xol-1 mutant XO animals would have a: a.Male gonad b.Hermaphrodite gonad c.Something in between d.No gonad

4. Now think about Drosophila. In which chromosomal combination would a loss of function mutation in the Sxl (sex lethal) gene be lethal? a.XX b.XY c.Neither d.Both

5. You are doing chromosomal analysis of an individual with two X chromosomes who appears externally male. You find that one of the X chromosomes contains a large translocation from the Y chromosome, containing the SRY gene. If you were able to look at multiple tissue samples from this individual’s gonad, you would expect to see: a.The gonadal cells have all differentiated into testis tissue b.The gonadal cells have all differentiated into ovarian tissue c.The gonadal cells have not differentiated into testis or ovarian tissue d.Some gonadal cells have differentiated into testis, some into ovarian tissue

6. Say there are approximately equal amounts of testicular and ovarian tissue in the gonad from the previous example. What characteristics would this person have? a. ductal system male, external male secondary sex characteristics b. ductal system male, external female secondary sex characteristics c. ductal system female, external female secondary sex characteristics d. ductal system female, external male secondary sex characteristics

7. Individuals with an XXY genotype are infertile because: a.Testes do not develop normally b.Cannot produce testosterone c.Cannot respond to AMH d.Extra X transcripts interfere with male fertility

8. If an XY individual contained an extra copy of the Xist region, translocated onto an autosome, what would happen? a.Their X chromosome would be inactivated b.The autosome with the Xist region would be inactivated c.The autosome would be inactivated sometimes; the X inactivated sometimes d.Neither would be inactivated, because there’s still only one X chromosome

9. How can both male and female mammals undergo normal development when they have different numbers of X chromosomes? a. Males need fewer of the X chromosome gene products than females. b. Both males and females only need one copy of most X chromosome genes. c. Genes on the X chromosome are activated differently in males and females. d. Males and females have different genes on their X chromosomes.

10. True/false. C. elegans and Drosophila use the same basic mechanism for dosage compensation, but differ as to which sex upregulates or downregulates the X chromosome.

11. True/false. Mammalian dosage compensation is controlled by the same genetic pathway as sex determination

12. True/false. Xist is primarily transcribed from the X chromosome that will be active.

13. A homozygous lf mutation in the dosage compensation gene sdc-2 will kill otherwise normal hermaphrodite but not male embryos. Consider double mutant embryos of the following four genotypes and phenotypes. Which two of them will die? a. sdc-2(0); tra-1(0) XX (male gonad) b. sdc-2(0); tra-1(0) XO (male gonad) c. sdc-2(0); her-1(0) XX (hermaphrodite gonad) d. sdc-2(0); her-1(0) XO (hermaphrodite gonad)

14. Suppose that an XX individual is heterozygous for a loss of function mutation in Xist. What result would you expect regarding X inactivation? a.Both X chromosomes are active b.Both X chromosomes are inactive c.X inactivation occurs non-randomly, on the chromosome with the Xist mutation d.X inactivation occurs non-randomly, on the wild type chromosome e.There is no effect on the inactivation of the X chromosomes