Question

Match the terms in column I with their description in column II and choose the correct option.

Answer 1

A pair of alleles generally define a character. The two alleles can be similar (homozygous) or dissimilar (heterozygous). In a heterozygous organism, if one allele expresses itself and dominates over the other, then it is termed as dominance. The allele which is unable to express is called the recessive allele.

But in a heterozygous organism when both alleles express themselves fully, it is called codominance. This is commonly seen in the AB blood group of humans.

When many genes govern a single character it is referred to as polygenic inheritance. Eg., Human skin colour

A single gene inheritance that influences many phenotypic expressions is called pleiotropy. In most cases it is the effect of a gene on metabolic pathways which results in different phenotypes. Example: phenylketonuria in humans. A mutation in a single gene (encoding phenylalanine hydroxylase) manifests in various phenotypic expressions such as mental retardation, hypopigmentation of skin and hypopigmentation of hair.