Exam 4 with answers Spring 2017.docx

Exam 4 with answers Spring 2017.docx - Genetics Name Spring...

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Genetics Name: Spring, 2017 Exam 4 Please turn off your cell phones. 1.) Recall that the nematode worm, C. elegans , has XX hermaphrodites and XO males, but no females. The XX hermaphrodites often self-fertilize. 99.9% of these offspring are also hermaphrodites, and ~0.1 % are males. A.) (4 pts) Draw the Punnett square for self-fertilization: X X X XX XX X XX XX The Punnett square could be smaller, eg 1 x 2 or even 1 x 1, since the rows and columns are redundant. B.) (4 pts) What process might explain how XO males arise from self-fertilization? (Hint: we have studied it recently in this class.) Non-disjunction for full credit. X inactivation for 1 pt only.
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2.) (12 pts) Triple-X human females typically have normal offspring. What kinds of gametes, with respect to the X chromosomes, would you expect from such XXX females? Draw meiotic stages that show the gametes that are expected to be produced. Draw one un-replicated X chromosome like this: Full credit includes replicated chromosomes, and the results after meiosis 1, meiosis 2. 3.) (9 pts) A small part of the human Y chromosome contains the gene that is responsible for determining maleness. What is the name of this gene? SRY When in the development of a human embryo is this gene active? Weeks 5-7 after fertilization. 6-8 weeks is OK. Under what condition might a human female have the XY sex chromosome complement? Aberrant recombination removes SRY from the Y chromosome. Or, SRY could be deleted from the Y chromosome. Or, there could be a loss-of-function mutation in SRY.
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4.) (6 pts) How many Barr bodies would one expect to see in cells of Turner syndrome females and Klinefelter syndrome males? Explain.
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