What is the difference between a dominant and recessive allele?

A dominant allele is expressed when present in a heterozygous individual, while a recessive allele is only expressed in homozygous individuals.

Genes are made up of alleles, which are alternative forms of a gene that code for different variations of a trait. Dominant alleles are expressed when present in a heterozygous individual, meaning they only need one copy of the dominant allele to be expressed. For example, if a person inherits a dominant allele for brown eyes from one parent and a recessive allele for blue eyes from the other parent, they will have brown eyes because the dominant allele is expressed.

On the other hand, recessive alleles are only expressed in homozygous individuals, meaning they need two copies of the recessive allele to be expressed. If a person inherits two copies of the recessive allele for blue eyes, they will have blue eyes because the recessive allele is expressed. However, if they inherit one dominant allele for brown eyes and one recessive allele for blue eyes, they will still have brown eyes because the dominant allele is expressed.

It is important to note that dominant alleles do not necessarily represent the most common allele in a population, nor are recessive alleles always rare. The expression of an allele depends on its interaction with other alleles and the environment. Understanding the difference between dominant and recessive alleles is crucial in predicting the inheritance patterns of traits and genetic disorders.