The term for different forms of a gene is called an allele. Alleles result from mutations or variations in the DNA sequence of a gene. Each individual carries two alleles for each gene, one inherited from each parent, and these can be identical (homozygous) or different (heterozygous). The combination of alleles determines the expression of specific traits, such as eye color or blood type. Genetic diversity among alleles within a population contributes to the variation in traits seen in organisms, playing a critical role in evolution and natural selection.