An allele is one of two or more versions of a DNA sequence at a specific location (locus) on a chromosome. Each individual inherits two alleles for each gene-one from each parent. These alleles can be identical (homozygous) or different (heterozygous)
. Alleles represent the different forms a gene can take, often differing by small changes in the DNA sequence, such as single nucleotide polymorphisms or insertions/deletions. While many alleles have little effect on gene function, some cause variations in observable traits, like eye color or blood type
. Alleles can be classified as dominant or recessive depending on how they influence traits. A dominant allele can determine a trait even if only one copy is present, whereas a recessive allele only affects the trait if both copies are recessive. Sometimes alleles show codominance, where both alleles contribute to the phenotype, as seen in the human ABO blood group system
. In summary, alleles are variant forms of a gene that contribute to genetic diversity and influence physical traits, disease risks, and other biological functions in organisms
