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Unformatted text preview: 504 Chapter 15 Large-Scale Chromosomal Changes expressed, then a deletion spanning the b 1 and c 1 genes has probably occurred on the other homolog. Because in such cases it seems as if recessive alleles are showing dominance, the effect is called pseudodominance. In the reverse caseif we already know the loca- tion of the deletionwe can apply the pseudodomi- nance effect in the opposite direction to map the posi- tions of mutant alleles. This procedure, called deletion mapping, pairs mutations against a set of defined over- lapping deletions. An example from the fruit fly (Drosophila) is shown in Figure 15-29. In this diagram, the recombination map is shown at the top, marked with distances in map units from the left end. The hori- zontal red bars below the chromosome show the extent of the deletions listed at the left. Each deletion is paired with each mutation under test, and the phenotype is ob- served to see if the mutation is pseudodominant. The mutation prune (pn) , for example, shows pseudodomi-...
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- Spring '08