Yhteisdominanssi

Yhteisdominanssi, a Finnish term, translates to "co-dominance" in English and refers to a mode of inheritance in genetics. In co-dominance, both alleles of a gene present in a heterozygous individual are fully and simultaneously expressed. This means that neither allele is dominant over the other, and both traits are visible in the phenotype.

A classic example of co-dominance is found in the coat coloration of certain cattle breeds, such as the Shorthorn. If a red Shorthorn cow is crossed with a white Shorthorn bull, their offspring will not be a blend of red and white, nor will they be entirely red or entirely white. Instead, the offspring will exhibit roan coloration, meaning they will have both red and white hairs. Both the allele for red coat color and the allele for white coat color are expressed equally.

Another well-known instance is the ABO blood group system in humans. The AB blood type is a result of co-dominance between the A allele and the B allele. Individuals with AB blood have both A and B antigens present on the surface of their red blood cells. Unlike incomplete dominance, where traits blend, or simple dominance, where one allele masks the other, co-dominance ensures that both contributing alleles contribute to the observable phenotype. This phenomenon is a fundamental concept in understanding Mendelian inheritance patterns and the diversity of traits in living organisms.