Alleles
Different forms of a gene
Alleles are the variants of a specific gene that are present in different individuals. Genes are made up of DNA, and each gene has a specific sequence of DNA that determines the traits that it codes for. These traits can differ between individuals based on the versions of the gene that they possess, which are called alleles.
An individual can inherit two copies of a gene, one from each parent, which means that they can have two copies of the same allele (homozygous) or two different alleles (heterozygous). In some cases, one allele may be dominant over the other, which means that it will be expressed in the phenotype, or physical appearance, of the individual. The recessive allele, on the other hand, will only be expressed if the individual has two copies of it.
For example, in humans, the gene for eye color has several different alleles, including the dominant brown allele and the recessive blue allele. A person who has two copies of the brown allele will have brown eyes, while a person who has two copies of the blue allele will have blue eyes. A person who is heterozygous, with one brown allele and one blue allele, will have brown eyes because the brown allele is dominant over the blue allele.
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