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How are homozygous and heterozygous animals different for a trait?
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Animal breeding
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In animal breeding, the distinction between homozygous and heterozygous animals is based on the pair of alleles an individual carries at a specific gene locus on its chromosomes.1
- Homozygous: An animal is homozygous for a trait if it possesses two identical alleles at a specific locus. Because both alleles are the same, the animal will pass that specific version of the gene to its offspring with certainty.213
- Heterozygous: An animal is heterozygous if it carries two different alleles at that locus. In this state, the animal’s physical appearance—or phenotype—depends on the dominance relationship between the two alleles.21
The expression of these traits can vary:
* Complete Dominance: One allele masks the other, making the heterozygote indistinguishable from the dominant homozygote.14
* Incomplete Dominance: The heterozygote displays a phenotype that is an intermediate blend of the two homozygous states.4
* Codominance: The heterozygote expresses the characteristics of both alleles simultaneously.14
Understanding these genetic states is essential for breeders to manage variation and improve livestock performance.1