Info

several generations, she discovered a mutation in her colony that produces yellow eyes, in contrast with normal red eyes, and Amanda determined that this trait is definitely X-linked recessive. Because yellow eyes are X linked, she assumed that either this species has the XX-XY system of sex determination with genic balance similar to Drosophila or it has the XX-XO system of sex determination.

How can Amanda determine whether sex determination in this species is XX-XY or XX-XO? The chromosomes of this species are very small and hard for Amanda to see with her student microscope, so she can only conduct crosses with flies having the yellow-eye mutation. Outline the crosses that Amanda should conduct and explain how they will prove XX-XY or XX-XO sex determination in this species.

Occasionally, a mouse X chromosome is broken into two pieces and each piece becomes attached to a different autosomal chromosome. In this event, only the genes on one of the two pieces undergo X inactivation. What does this observation indicate about the mechanism of X-chromosome inactivation?

SUGGESTED READINGS]_

Allen, G. E. 1978. Thomas Hunt Morgan: The Man and His Science. Princeton, NJ: Princeton University Press. An excellent history of one of the most important biologists of the early twentieth century.

Bogan, J. S., and D. C. Page. 1994. Ovary? Testis? A mammalian dilemma. Cell 76:603 - 607.

A concise review of the molecular nature of sex determination in mammals.

Bridges, C. B. 1916. Nondisjunction as proof of the chromosome theory of heredity. Genetics 1:1 - 52.

Bridges's original paper describing his use of nondisjunction of X chromosomes to prove the chromosome theory of heredity.

Foster, E. A., M. A. Jobling, P. G. Taylor, P. Donnelly, P. de Knijff, R. Mieremet, T. Zerjal, and C. Tyler-Smith. 1998. Jefferson fathered slave's last child. Nature 396:27- 28. Report on the use of Y-linked markers to establish the paternity of children of Thomas Jefferson's slave.

Kohler, R. E. 1994. Lords of the Fly: Drosophila Genetics and the Experimental Life. Chicago: University of Chicago Press. A comprehensive history of Drosophila genetics from 1910 to the early 1940s.

Marx, J. 1995. Tracing how the sexes develop. Science 269: 1822 -1824.

A short, easy-to-read review of research on sex determination in fruit flies and the worm Caenorhabditis elegans.

McClung, C. E. 1902. The accessory chromosome: sex determinant. Biological Bulletin 3:43 - 84. McClung's original description of the X chromosome.

Morgan, T. H. 1910. Sex-limited inheritance in Drosophila. Science 32:120-122. First description of an X-linked trait. Penny, G. D., G. F. Kay, S. A. Sheardown, S. Rastan, and N. Brockdorff. 1996. Requirement for Xist in X chromosome inactivation. Nature 379:131 - 137.

This article provides evidence that the XIST gene has a role in X-chromosome inactivation. Ryner, L. C., and A. Swain. 1995. Sex in the 90s. Cell 81:483 - 493.

A review of research findings about sex determination and dosage compensation. Thomas, M. G., T. Parfitt, D. A. Weiss, K. Skorecki, J. F. Wilson, M. le Roux, N. Bradman, and D. B. Goldstein. 2000. Y chromosomes traveling south: the Cohen modal haplotype and the origins of the Lemba — the "Black Jews of Southern Africa." American Journal of Human Genetics 66:674 - 686. A fascinating report of the use of Y-linked genetic markers to trace the male ancestry of the Lemba tribe of South Africa.

Williams, N. 1995. How males and females achieve X equality. Science 269:1826-1827.

A brief, readable review of recent research on dosage compensation.

0 0

Post a comment