Question

In the cross MMnn X mmNN, what proportion of the resulting F1 would be homozygous dominant for both genes?

Firstly, what does this question even mean? And I tried working this out using the punnet square but failed miserably, please help.

Answer 1

Parents MMnn and mmNN can producetwo types of gametes: Mn and mN. Therefore, their offspring are heterozygous: MmNn. That means that all hybrids have two different alleles of the gene: dominant M and recessive m; dominant N and recessive n. None of the resulting hybrids (0%) will be homozygous, either recessive mmnn, or dominant MMNN.