BIO207H5 Chapter 5.1: Linked Genes Do Not Assort Independently
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Reversion studies were done by exposing m- mutants to three mutagens: 5-bromouracil (BU) (causes AT->GC or GC->AT transitions), hydroxylamine (HA) (causes GC->AT transitions), and an acridine dye (small insertions or deletions). The resulting frequencies of wild-type revertants were compared with the spontaneous frequencies in the table below:
Revertants per 108 nuclei
Mutant | Spontaneous | BU | HA | Acridine |
a2 | 1.5 | 28.1 | 1.1 | 1.9 |
a4 | 1.2 | 1.8 | 1.9 | 40 |
a6 | 80 | 670 | 912 | 75 |
a8 | 5.0 | 5.0 | 5.1 | 5.1 |
Assume reversion takes place in the same gene originally mutated. What was the nature of the mutational event that gave rise to the mutants in the first place (i.e., the m+ -> m- event)? Be as specific as possible (e.g. if a transition then was it AT->GC or GC->AT or canât be determined which direction) based on the data presented, and ignore the possibility of transposable element mutations.
a2__________________________
a4__________________________
a6__________________________
a8__________________________