Gene A encodes a receptor tyrosine kinase; Gene B encodes a G-protein coupled receptor. Each of such genes has mutant alleles which are structurally normal however lack activity in their cytoplasmic domains.

Q1. What activity does the cytoplasmic domain of a receptor tyrosine kinase generally encompass?

Q2. What activity does the cytoplasmic domain of the G-protein-coupled receptor generally encompass?

Q3. Is heterozygosity for the mutant allele of gene A or gene B likely to be more serious?  describe why?