Scott_Handout8-key - 3/29/2010 MCB 104; Handout #8 1A. In...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
3/29/2010 MCB 104; Handout #8 1A. In Drosophila , will mutations that prevent the functioning of the dosage compensation machinery be lethal in males, females, or both? Explain. Males. Drosophila dosage compensate by increasing the expression of X-linked genes in males. So without dosage compensation, females would have a normal (2x) dose of X- linked genes, but males would only have a one-half dose (1x) of X-linked genes, and not survive. 1B. In C. elegans , will mutations that prevent the functioning of the dosage compensation machinery be lethal in males, hermaphrodites, or both? Explain. Hermaphrodites. C. elegans dosage compensate by decreasing the expression of genes on each of the X chromomosome in hermaphrodites. Without dosage compensation, males would have a normal dose of X-linked genes (1x), but hermaphrodites would have a double dose (2x), and would not survive. 1C. In mammals, will deletion of the X inactivation center be lethal to males, females, or both? Lethal to females—provided the X inactivation center is mutant on both X’s. If at least one X has an X inactivation center, it can be silenced and form a Barr body, and therefore allow the female to dosage compensate (and only have a single dose of X-linked genes). However, if a female cannot silence either X chromosome, she will have a double dose of X-linked genes, which will most likely be lethal. Males would not be adversely affected by a deletion of the X inactivation center. 1D. What is the Lyon hypothesis? If a human female is heterozygous for the deletion of an X-linked gene that is essential for the survival of toenail cells, what will be her profile of X chromosome inactivation in toenail cells? Lyon Hypothesis: In each cell, one X chromosome is randomly silenced to form a Barr body. The X that is silenced will be silenced in all progeny of the original cell (i.e. the whole cell lineage will have the same silenced X chromosome). All of the toenail cells will have silenced the X that carries the deletion of the toenail- essential gene. This way, the toenail cells will be expressing genes from the wild-type X, and thus will express the gene that is essential for toenail development. The precursor cells might have been heterogeneous for X inactivation, but the cells that
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 4

Scott_Handout8-key - 3/29/2010 MCB 104; Handout #8 1A. In...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online