Chromosomes, Genes, and Alleles Explained Simply

What are alleles?Alleles are different versions or variants of the same gene.Each gene can have multiple allele forms that code for variations of the same trait.Alleles arise through mutations in the DNA sequence, creating small differences in the genetic code.For example, the gene for eye color has multiple alleles that can result in blue, brown, green, or other eye colors.Since humans have two copies of each chromosome, one from each parent, we have two alleles for each gene.We inherit one allele from our mother and one from our father, forming a pair of alleles for each gene.These two alleles can be identical, known as homozygous, or different, called heterozygous.This combination of alleles influences how specific traits are expressed in an individual.Dominant and recessive alleles determine how traits are expressed when different versions of a gene are present.When a gene has two different alleles, one may be dominant over the other.A dominant allele will express its trait even when paired with a different allele.A recessive allele's trait is only expressed when two copies of that allele are present.Eye color is a classic example. The allele for brown eyes, represented by capital B, is dominant over the allele for blue eyes, represented by lowercase b.There are three possible combinations of these alleles, resulting in different eye colors.A person with either two dominant brown-eye alleles or one brown and one blue allele will have brown eyes.For the recessive blue eye trait to appear, a person must inherit two blue-eye alleles, one from each parent.This relationship between dominant and recessive alleles explains why some traits can appear to skip generations.A recessive trait like blue eyes can appear to skip generations when carriers, who have brown eyes but carry the blue eye allele, have children.This three-generation family tree shows how blue eyes can appear in the first and third generations, even when the middle generation has brown eyes.