Question

Match the genetic phenomena with their respective ratios.

a	Inhibitory gene ratio	1	9 : 3 : 4
b	Complementary gene ratio	2	1 : 1 : 1 : 1
c	Recessive epistasis ratio	3	12 : 3 : 1
d	Dihybrid test cross ratio	4	13 : 3
e	Dominant epistasis ratio	5	9 : 7

• A. a- 5, b- 4, c- 3, d- 2, e- 1
• B. a- 4, b- 5, c- 1, d- 2, e- 3
• C. a- 1, b- 2, c- 4, d- 3, e- 5
• D. a- 2, b- 1, c- 4, d- 5, e- 3
• E. a- 5, b- 4, c- 1, d- 2, e- 3

Answer 1

Answer: (B)

a- 4, b- 5, c- 1, d- 2, e- 3

When one gene inhibits the expression of other; the dominant alleles of one gene (A) in homozygous and heterozygous (AA, Aa) condition and homozygous recessive alleles bb of another gene (B) produce the same phenotype. Here, the rest genotypes produce contrasting phenotype; thus only two phenotypes. The resultant F${}_2$ ratio is 13: 3. Complementary genes are the non-allelic 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. Dominant epistasis is the non-allelic gene interaction where the presence of one dominant gene masks the expression of another dominant gene, dihybrid ratio becomes 12:3:1. A dihybrid test cross is performed between dihybrid and double recessive genotype, for example, a cross between TtRr and ttrr, which gives 1:1:1:1 ratio. Recessive epistasis is the nonallelic gene interaction where the presence of one recessive gene masks the expression of another recessive gene, dihybrid ratio becomes 9 : 3 : 4.