Question

1 : 2 : 1 phenotypic and genotypic ratios occur in the case of

• A. Blending inheritance
• B. Pseudoalleles
• C. Multiple alleles
• D. Complementary genes

Answer 1

The correct option is A Blending inheritance

Law of incomplete dominance tells that where none of the factors of a gene is dominant, the phenotype of the heterozygous dominant individual is a blend of dominant and recessive traits. For example, flower color in Mirabilis jalapa shows incomplete dominance and the monohybrid cross between two pure varieties gives 1:2:1 phenotypic ratio in F${}_2$ generation which is 3:1 in dominant traits. Pseudoalleles are the genes that functionally behave as allelic pairs but structurally they are different genes, not allelic pairs. Multiple alleles mean the presence of more than two alleles of a gene; for example, ABO blood group inheritance is governed by three alleles of I gene namely $I^A$, $I^B$ and $I^O$. The ratio of a cross of multiple alleles and pseudogenes depends on their recessive-dominance relationship. 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. Thus, the correct answer is option A.