What is incomplete dominance?

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In the field of genetics, incomplete dominance basically refers to cases wherein one allele or part of one gene is unable to dominate the other allele when combined together. This condition is also referred to as partial domination wherein neither one allele is able to dominate the other in terms of its genetic properties and characteristics. When two different genes are combined and there is incomplete dominance, a third so-called phenotype will then be created as a result. This third phenotype will typically share the characteristics and genetic properties of the two original genes or alleles.

Co-dominance is similar to incomplete dominance in the sense that the result is a third phenotype. The main difference is that in co-dominance both original genes are copied or expressed completely in the resulting phenotype. This is what happens to combining blood types A and B and the result being the AB blood type. A typical example of incomplete dominance is when a baby is born having wavy hair when one parent has straight hair while the other has curly hair. The genes of both parents have combined but are unable to completely dominate each other. The offspring or baby has all the chances to inherit either the straight hair or the curly one. In incomplete dominance, the inheritance is basically shared in the form of wavy hair. The same concept can also be applied to dog or cat breeding. When a black male dog for example is paired with a white female, the puppies may share both parents genes and have a striped or brindle coat because of incomplete dominance of either parents’ genes.

Incomplete dominance may also be applied to cross-pollination in plants. Carnations for example grow in different colors. The pink variety is actually a result of incomplete dominance between the red and white carnation varieties. Neither one of the red and white alleles of the carnation plant are able to completely dominate each other when they cross-pollinate to reproduce. The basic result will then be pink carnation which is a shared genetic characteristic of the original white and red carnation alleles.