Allele

What is an Allele?

An allele is one of the alternative forms or versions of a gene found at a specific location on a chromosome. Genes code for specific traits, and each gene can have different variations, known as alleles.

Alleles arise due to genetic variations, which can be caused by mutations or recombination during sexual reproduction.

Alleles and Genetics

Gene Variations

Genes are segments of DNA that provide the instructions for building and maintaining the components of living organisms. Different versions of a gene, representing variations in the DNA sequence, are called alleles.

Alleles and Homologous Chromosomes

Humans have two sets of chromosomes, one from each parent. Genes are located at specific positions on chromosomes, and the alleles of a gene are found at corresponding locations on homologous chromosomes.

Dominant and Recessive Alleles

Alleles can be classified as dominant or recessive based on their effects on an organism’s phenotype (observable traits). Dominant alleles mask the expression of recessive alleles when both are present in a heterozygous individual.

Genotype and Phenotype

The combination of alleles an individual possesses for a particular gene is known as its genotype. The observable characteristics or traits resulting from the genotype are called the phenotype.

Homozygous and Heterozygous

If an individual has two identical alleles for a particular gene (e.g., AA or aa), they are said to be homozygous. If an individual has two different alleles for a gene (e.g., Aa), they are considered heterozygous.

Genetic Variation

Allelic variation contributes to genetic diversity within populations. Mutations, genetic recombination, and other mechanisms can give rise to new alleles over time.

Blood Type Alleles

The gene responsible for determining human blood type has three main alleles: A, B, and O.
Individuals inherit one allele from each parent, resulting in different blood type combinations (e.g., AA, AO, BB, BO, OO).