Question

Why single recessive gene cannot decide appearance?

Answer 1

Recessive alleles are usually caused by a loss of function in the protein they encode for. This can be as subtle as a single, critical amino acid being swapped to a different amino acid, or as dramatic as something that causes an early stop codon and thus no protein to be made. If a cell is heterozygous for a loss of function allele (that is, one gene copy makes functional protein and the other one doesn't), it's still making some functional protein and may not behave any differently. However, if both copies are not making functional protein, that protein's activity is completely missing and a behavioral change is likely. So in an allele if single gene is recessive the other must be dominant gene having high functions for the proteins coding so it will determine the appearence.If both are recessive genes in alleles, then the organism will appear as recessive ; then only the recessive gene can decide appearence.

Hence, single recessive gene cannot decide appearance