2006 exam IV answers

2006 exam IV answers - Page 1 Name:ANSWERS Biology 52 exam...

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Page 1 Name: ANSWERS Biology 52 exam IV, May 5, 2006 You have two hours. Feel free to draw pictures to help answer the questions. Bear in mind that some questions may cover material covered in 2006 but not this year. 1) [8 points] Suppose that you are designing a screen for mutants affecting embryonic patterning in Drosophila. You treat a population of male flies with a chemical mutagen. a) Outline what you would then do to find individual flies with mutations of interest, starting with this mutagenized population and as many wild-type flies as you want. Include in your description which flies are heterozygous or homozygous for the new mutations you are screening for. Cross the mutagenized population to wild-type females (to transmit each new mutation), and cross the F1 progeny from these crosses to wild-type flies again (to obtain multiple male and female siblings each carrying the mutation). Mate F1 males and females from the same family (i.e. potentially carrying the same mutations) to obtain homozygous progeny (25% of progeny of matings between two carriers). b) Some of the mutations you might find would have a maternal effect. How would you recognize individuals with maternal-effect mutations? Look for females that produce progeny with defective development, even when crossed with a wild-type male. 2) [20 points] The embryonic patterning defects of some Drosophila mutants can be rescued by injections of cytoplasm from wild-type embryos. How would each of the following embryos develop: a) bicoid mutant embryo (from a bicoid mutant mother): i) untreated – no anterior end ii) injected at the anterior end with cytoplasm from the anterior end of a wild-type embryo would restore normal development iii) injected in the middle with cytoplasm from the anterior end of a wild-type embryo would have anterior structures in the middle, with anterior-posterior polarity in both directions toward the two ends b) toll mutant embryo (from a toll mutant mother): i) untreated – would be dorsalized ii) injected on the dorsal side with cytoplasm from the dorsal side of a wild-type embryo would not rescue ii) injected on the dorsal side with cytoplasm from the ventral side of a wild-type embryo would restore a ventral side, but on the “top” instead of the normal ventral side
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2006 exam IV answers - Page 1 Name:ANSWERS Biology 52 exam...

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