Phenotypic expressions depend upon conditions of development. It should live longer, for example. Restrictive conditions kill the individuals and permissive conditions allow it to live. Cancer is an example of a conditional mutant condition that depends upon multiple loci. Also, cancer may be produced both by multiple mutation, or by somatic crossing over.
Mutations occur at rates characteristic of loci , and the type of mutational change .
Where detailed experiments have been possible, the mutation rate varies greatly within a locus. Some loci are rarely seen in a mutant state. Others have many mutant alleles present. Generally, loci that are vital to survival and reproduction have low incidence of mutation, and vice versa . Similarly, the differences among related species are greatest for loci that are not essential to survival and reproduction.