1. X-rays are used to induce mitotic recombination in Drosophila females that have the genotype y+/+sn (y = yellow and sn = singed; y is closer to the centromere).

1. How does the rate of mitotic recombination relate to the frequency at which mosaic patches are seen? 

2. What phenotypes of mosaic patches are possible? 

3. What is the relative frequency of twin spot to single spot clones? 

2. In considering the production of twin spots:

   1. Is the cis or trans configuration better? 

   2. What is the effect of the position of the markers relative to the centromere? 

   3. What is the effect of the position of the markers relative to each other? 

   4. From your answers and from the reading and lectures make a list of the criteria you would use in choosing markers for mosaic analysis. 

3. How could you determine whether a mutation in Drosophila that caused nondisjunction in meiosis had a similar effect on somatic divisions? 

4. You are trying to examine the focus of action of a dominant mutation M in Drosophila and wish to look at genetic mosaics. A partial genetic map showing the centromere C. and the relative positions of M and a number of genes represented by recessive mutations (a, b, c, and d) is:

1. What is meant by "focus of action?" 

2. Which configuration (cis or trans) would you use to obtain twin spot mosaics using M and any one of the recessive mutations (assuming that twin spots could be made)? Why? 

3. Under what conditions would you not expect to see twin spots with either the cis or trans configuration? 

4. Using the configuration you chose in (b), what proportion of the mitotic recombinations that could give rise to a twin spot do you expect will actually do so? Explain your answer. 

5. Which marker mutation (a, b, c, or d) would you use with M to optimize the number of twin-spot relative to single-spot mosaics? Why? 

6. Would the answers to Parts b-e differ if M was a recessive mutation and the other marker mutations were dominant?

5. Define and distinguish briefly between each set of the following pairs

   1. Fate map versus meiotic map

   2. twins spot and single spot mosaics

   3. Gene expression studies using mosaic analysis vs. gene expression studies using green fluorescent protein (GFP)

7. Describe a genetic (not molecular) experiment to determine how near the eye and antenna are on the fate map of the Drosophila blastoderm.

8. Answer TRUE or FALSE.  If the statement is TRUE, explain or give a supporting example.  If the statement is FALSE, either correct the statement or give a counterexample.

   1. The production of gynandromorphs in Drosophila demonstrates that sex determination in this species is cell autonomous.

   2. The production of twin spots involving two recessive mutations (a and b) requires that recombination occurs between a and b.

Answers