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| Modern Genetic Analysis Chapter 7. Gene Mutations Mutational Analysis Figure 7-37. (a) Mutation m has completely lost its function (it is a null mutation). In the heterozygote, wild-type gene product is still being made, and often it is enough to result in a wild-type phenotype, in which case, m acts as a recessive. If the wild-type gene product is insufficient, the mutation is seen as dominant. (b) Mutation m still retains some function, but in the homozygote there is not enough to produce a wild-type phenotype. (c) Mutation M has acquired a new cellular function represented by the gene product colored yellow. M is expressed in the heterozygote and most likely acts as a dominant. The homozygous mutant may or may not be viable, depending on the role of the + allele.

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