Problem Set 7

Biological Sciences 355
Honors Genetics


Problem Set 7

The following problems are to help you sharpen and deepen your understanding of how to map with deletions and point mutations. These questions will be discussed in recitation on Oct. 24


1. (From Griffiths et al., Introduction to Genetic Analysis, Chap. 12) The following map shows four deletions (1 to 4) involving the rIIA cistron of bacteriophage T4:

Five point mutations (a to e) in rIIA are tested against these four deletion mutants for their ability to give r+ recombinants. In the following results "+" indicates that some wt recombinants were observed and "-" indicates that no wt recombinants were observed:
a b c d e
1++-++
2++---
3--+-+
4+-+++

What is the order of the point mutations? How do you know that your solution is unique?

2. (From Griffiths et al., Chap. 12) In a phage, a set of deletions is intercrossed in pairwise combinations. The following results are obtained ("+" indicates some wt recombinants are obtained):

12345
1-+-+-
2+-++-
3-+---
4++--+
5---+-

Construct a deletion map from this table. How do you know that your solution is unique?

3. (From Griffiths et al., Chap. 12) You have the following map of the rII locus:

where the locations of point mutations are indicated below the line. You find a new mutation (rW) and find that it does not complement any of the other A or B mutations. You find that wt recombinants are obtained in crosses with rX, rY, rE and rF, but not with rZ or rD. Suggest several possible explanations for these results and suggest tests you might use to distinguish among your hypotheses. Give careful attention to any control experiments that might be required.

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This information was prepared for Fall Term 2008. Report broken links or comments to: Dr. Lewis Jacobson