Q. The gene which masks the effect of another gene is called :
(a) Epistasis
(b) Lethal gene
(c) Multiple allele
(d) Complementary gene
Solution :
Correct option : A Epistasis is the non-allelic gene interaction where the presence of one gene masks the expression of another gene; dihybrid ratio for dominant epistasis becomes 12:3:1. Recessive epistasis is the non-allelic gene interaction where the presence of one recessive gene masks the expression of another recessive gene, dihybrid ratio becomes 9 : 3 : 4. Multiple alleles mean presence of more than two alleles of a gene which can be dominant, incompletely dominant or codominant; for example, ABO blood group inheritance is governed by three alleles of I gene namely IA, IB and IO. Complementary genes are the nonallelic genes which have their independent effect but produce a new trait when their dominant forms are present together. A dihybrid cross of complementary genes gives 9:7 phenotypic ratio. The genes that cause premature death of the organism are called lethal genes. If the gene is dominant, it kills heterozygotes, whereas recessive lethal genes kill homozygous recessive individuals. The correct option is A.
