3. Expression of Phenotype

Allele

One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

Codominance

A genetic scenario where both alleles in a heterozygote are expressed independently, making both parental traits recognizable in the phenotype.

Dominant Allele

An allele that has an effect on the phenotype when combined with a recessive one (Rr) or when homozygous (RR).

Glycoprotein

A protein with a carbohydrate attached; in the ABO blood system, these are found on the membranes of red blood cells.

Heterozygous

Having two different alleles for a particular gene.

Homozygous

Having two identical alleles for a particular gene.

Incomplete Dominance

A pattern of inheritance where the action of one allele does not completely mask the other, resulting in an intermediate, "blended" phenotype in heterozygotes.

Multiple Alleles

A genetic system where more than two alleles exist for a single gene, such as in human blood.

Phenotype

The observable physical or biochemical characteristics of an organism, determined by both genetic makeup and environmental influences.

Recessive Allele

An allele that only has an effect on the phenotype when present in a homozygous state.

Roan

A phenotype in cattle characterized by a mixture of red and white hairs equally distributed across the body, resulting from codominance.