What are Alleles?

Alleles are different forms of a gene that can lead to different traits in an organism. They are inherited from the organism's parents and are located at the same position on a pair of homologous chromosomes.

Dominant and Recessive Alleles

Alleles can be dominant or recessive. Dominant alleles mask the expression of recessive alleles. For example, if an organism inherits one dominant allele and one recessive allele for a particular trait, the dominant allele will determine the trait expressed in the organism.

Allele Interactions

Alleles can interact in different ways. Incomplete dominance occurs when neither allele is completely dominant and the heterozygous individual expresses a phenotype that is a blend of the two alleles. Codominance occurs when both alleles are expressed in the heterozygous individual, resulting in a phenotype that shows traits from both alleles.

Multiple Alleles

Some genes may have multiple alleles, meaning there are more than two possible forms of the gene. However, an individual organism can only have two alleles for a particular gene, as they receive one allele from each parent.

Examples of Alleles

One classic example of alleles is the gene for flower color in pea plants, where the allele for purple flowers is dominant over the allele for white flowers. Another example is the ABO blood group system in humans, which is determined by three alleles: IA, IB, and i.