What are alleles, and how do they represent various specific forms of a gene?

Sourav PanNovember 8, 2024

Answered

Alleles are defined as variant forms of a gene that occupy the same position, or locus, on a chromosome. Each gene can have multiple alleles, which contribute to the genetic diversity observed in traits among individuals.

Key Characteristics of Alleles

• Variants of a Gene: Alleles represent different versions of the same gene. For example, the gene responsible for eye color may have several alleles, such as those coding for blue, brown, or green eyes. These variations arise from differences in the nucleotide sequences at the specific locus where the gene is located on a chromosome.
• Homozygous and Heterozygous: An individual inherits two alleles for each gene—one from each parent. If both alleles are identical, the individual is said to be homozygous for that gene (e.g., AA or aa). If the alleles are different, the individual is heterozygous (e.g., Aa). The combination of these alleles determines the organism’s genotype, which influences its observable traits or phenotype.
• Dominance and Recessiveness: Alleles can exhibit different relationships in terms of dominance. A dominant allele will mask the effect of a recessive allele when present in a heterozygous genotype. For instance, if “A” represents a dominant allele for brown eyes and “a” represents a recessive allele for blue eyes, individuals with genotypes AA or Aa will have brown eyes, while only those with aa will have blue eyes.
• Multiple Alleles: Some genes can have more than two alleles in a population, leading to multiple phenotypic expressions. A classic example is the ABO blood group system in humans, where three alleles (IA, IB, and i) determine blood type compatibility