Homozygous

A cell is said to be homozygous for a particular gene when identical alleles of the gene are present on both homologous chromosomes.^[2]

An individual that is homozygous-dominant for a particular trait carries two copies of the allele that codes for the dominant trait.

This allele, often called the "dominant allele", is normally represented by the uppercase form of the letter used for the corresponding recessive trait (such as "P" for the dominant allele producing purple flowers in pea plants).

When an organism is homozygous-dominant for a particular trait, its genotype is represented by a doubling of the symbol for that trait, such as "PP".

An individual that is homozygous-recessive for a particular trait carries two copies of the allele that codes for the recessive trait.

This allele, often called the "recessive allele", is usually represented by the lowercase form of the letter used for the corresponding dominant trait (such as, with reference to the example above, "p" for the recessive allele producing white flowers in pea plants).

The genotype of an organism that is homozygous-recessive for a particular trait is represented by a doubling of the appropriate letter, such as "pp".