When two mutant alleles of a gene are brought into the same cell, the merodiploid might acquire a wild-type phenotype by intragenic complementation or by recombination. How could you distinguish between these two possibilities?


If the donor copy of a gene had a nonsense mutation in a particular base pair and the recipient had a base substitution mutation located one base pair away, could the gene be repaired by recombination?

ANSWER: Recombination occurs by cutting and rejoining at the phosphate bond between two base pairs. Thus reciprocal recombination between the two adjacent pairs would yield a wild-type recombinant at both base pairs and the corresponding double-mutant recombinant. [Get a pencil and a piece of paper and try drawing it out!]

Sometimes interference between closely spaced recombination events (cross-overs) results in disagreement between the gene order predicted from two-factor and three-factor crosses for very closely linked mutations. Suggest two different in vivo recombination experiments that would allow you to figure out the gene order.


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Last modified October 18, 2004