Penetrance & Genetics

In the nematode C. elegans, homozygosity for the “b” mutant allele causes a blister phenotype, where the adult worm forms blisters on its outer cuticle. Examination of 100 individuals with genotype b/b reveals that 58 of them have blisters, 42 show a completely wild-type phenotype (no blisters on the cuticle). These observations suggest that:

    a.   b has complete penetrance but a high environmental component

    b.   b has incomplete penetrance

    c.   b has variable penetrance

    d.   b is on the X chromosome, assuming worms show X inactivation

    e.   wildtype individuals are due to spontaneous mutations