Allele

Allele

Each gene may exist in alternative forms known as alieles, which code for different versions of a particular inherited character. We may also define alleles as genes occupying corresponding positions on homologous chromo-somes and controlling the same characteristic (e.g. height of plant) but producing different effects (tall or short). The term homologous refers to chromosomes that carry the same set of genes in the same sequence, although they may not necessarily carry identical alleles of each gene.

Wild-type vs Mutant alleles

Prevalent alleles in a population are called wild-type alleles. These alleles typically encode proteins that are made in the right amount and function normally. Alleles that are present at less than 1% in the population and have been altered by mutation are called mutant alleles. Such alleles usually result in a reduction in the amount or function of the wild-type protein and are most often inherited in a recessive fashion.

Dominant and Recessive alleles

A dominant allele masks or hides expression of a recessive allele and it is represented by an uppercase letter. A recessive allele is an allele that exerts its effect only in the homozygous state and in heterozygous condition its expression is masked by a dominant allele. It is represented by a lowercase letter.

Homozygous and Heterozygous

Each parent (diploid) has two alleles for a trait they may besdo

1. Homozygous, indicating they possess two identical alleles for a trait.

a. Homozygous dominant genotypes possess two dominant alleles for a trait (TT).

b. Homozygous recessive genotypes possess two recessive alleles for a trait (tt).

2. Heterozygous genotypes possess one of each allele for a particular trait (Tt).