Dumpy” is a commonly used mutant phenotype in the nematode worm, C. elegans. Two “dumpy” individuals are crossed to each other, and this cross produces 210 “dumpy” and 68 wild-type individuals. This indicates that the dumpy mutant trait is a dominant trait, and the mutants were heterozygous. The ratio of the two numbers is of the form, 3:1. This result can be reproduced by the following cross in Punnett Square, as shown in the image 1, where 'D' denotes dumpy trait and 'd' denotes wild type form.
Now, when a heterozygous dumpy mutant is crossed with a homozygous wild type nematode, the following genotypes are produced, two of Dd (dumpy) and two of dd (wild type), shown in image 2. The ratio of mutant to wild type in the offspring will be 2:2 or 1:1.
