An organism has a gene 'X'. Its dominant allele expresses character C-1 while its recessive allele expresses character C-2. This dominant allele is completely dominant over the recessive allele. It has another gene 'Y' which in its dominant form doesn't allow any expression of gene 'X'. Which of these genotypes of that organism will produce character C-1?

Question

An organism has a gene 'X'. Its dominant allele expresses character C-1 while its recessive allele expresses character C-2. This dominant allele is completely dominant over the recessive allele. It has another gene 'Y' which in its dominant form doesn't allow any expression of gene 'X'. Which of these genotypes of that organism will produce character C-1? (A) xxyy or XxYy (B) XXYY or XxYY (C) XxYy or XXYy (D) Xxyy or XXyy

Tardigrade Admin · Accepted Answer

This is an example of dominant epistatsis. Here, Y is the epistatic gene. In its dominant form that is YY or Yy it will not allow expression of X. That means for expression of X, the genotype should be yy. C-1 is dominant character expressed by gene X. Hence, C-1 can be expressed by genotypes XX or Xx. Thus, organisms which express character C-1 have genotype XXyy or Xxyy.