How do genes and alleles influence traits in domestic animals?

In domestic animals, genes and alleles are the fundamental units of heredity that determine an organism's phenotype—the observable traits such as size, color, and shape.1

The Role of Genes and Alleles

A gene occupies a specific location, or locus, on a chromosome. Alleles are alternative forms of these genes that occur at the same locus. An animal's genotype is the specific combination of alleles it carries.12
* Homozygous: The paired alleles are identical.12
* Heterozygous: The paired alleles are different.12

Expression of Traits

When alleles are paired, their interaction dictates how a trait is expressed:
* Dominant and Recessive: A dominant allele masks the expression of a recessive allele in a heterozygous pairing.12
* Codominance: Neither allele is dominant, and both may be expressed simultaneously.12

Genetic Variation in Breeding

Breeders utilize genetic variation to improve livestock. This variation is categorized by how genes act:
* Additive: The effect of each allele adds to the others at the same locus. This is the most useful form of variation for breeders because gains are permanent and cumulative.1
* Dominance: More complex to control because one allele masks another, making it difficult to distinguish between genotypes.1
* Epistatic: Involves the joint effects of genes at two or more loci; it is rarely used in breeding due to its complexity.1

While genetics provide the potential for traits, environmental factors often have a significant impact on the final performance of domestic animals, sometimes exceeding the influence of genetic differences.13