17. Mutation, Repair, and Recombination

A geneticist searching for mutations uses the restriction endonucleases SmaI and PvuII to search for mutations that eliminate restriction sites. SmaI will not cleave DNA with CpG methylation. It cleaves DNA at the restriction digestion sequence↓5′−CCC GGG−3′3′−GGG CCC−3′↑PvuII is not sensitive to CpG methylation. It cleaves DNA at the restriction sequence↓5′−CAG CTG−3′3′−GTC GAC−5′↑What common feature do SmaI and PvuII share that would be useful to a researcher searching for mutations that disrupt restriction digestion?

In a mouse-breeding experiment a new mutation called Dumbo is identified. A mouse with the Dumbo mutation has very large ears. It is produced by two parental mice with normal ear size. Based on this information, can you tell whether the Dumbo mutation is a regulatory mutation or a mutation of a protein-coding gene? Why or why not?

Considering the Dumbo mutation in Problem 37, what kinds of additional evidence would help you determine whether Dumbo is a mutation of a regulatory sequence or of a protein-coding gene?

Thinking back to the discussion of gain-of-function and loss-of-function mutations in Section 4.1, and putting those concepts together with the discussion of base substitution mutations in this chapter, explain why gain-of-function mutations are often dominant and why loss-of-function mutations are often recessive. Give an example of a type of gain-of-function mutation that is dominant and of a loss-of-function mutation that is recessive.