How do dominant and recessive alleles relate to phenotype expression?

Dominant alleles are expressed in the phenotype when present, while recessive alleles are only expressed in the absence of a dominant allele.

Genes are segments of DNA that code for specific traits. Each gene has two alleles, one inherited from each parent. The dominant allele masks the expression of the recessive allele, so only the dominant allele is expressed in the phenotype when present. For example, if a person inherits a dominant allele for brown eyes and a recessive allele for blue eyes, they will have brown eyes because the dominant allele masks the expression of the recessive allele.

Recessive alleles are only expressed in the phenotype when both alleles are recessive. This is known as homozygous recessive. For example, if a person inherits two recessive alleles for blue eyes, they will have blue eyes because there is no dominant allele to mask the expression of the recessive allele.

It is important to note that the presence of a dominant allele does not necessarily mean that the trait will be expressed in the phenotype. Some dominant alleles are only expressed in certain conditions or when paired with specific alleles. Additionally, some traits are influenced by multiple genes and their interactions, making the expression of the phenotype more complex.

Understanding the relationship between dominant and recessive alleles is essential in predicting the inheritance of traits and diagnosing genetic disorders.