Question

How do incomplete dominance, codominance, polygenic inheritance and pleiotropy, deviate from Mendel's observation?Give an example of each.

Answer 1

Incomplete dominance:- Mendel’s results were groundbreaking partly because they contradicted the (then-popular) idea that parents' traits were permanently blended in their offspring. In some cases, however, the phenotype of a heterozygous organism can actually be a blend between the phenotypes of its homozygous parents. For example, in the snapdragon, Antirrhinum majus, a cross between a homozygous white-flowered plant (C^WC^WC WC W ) and a homozygous red-flowered plant (C^RC^RC R C R) will produce offspring with pink flowers (C^RC^WC R C W ). This type of relationship between alleles, with a heterozygote phenotype intermediate between the two homozygote phenotypes, is called incomplete dominance. Codominance:- Closely related to incomplete dominance is codominance, in which both alleles are simultaneously expressed in the heterozygote. We can see an example of codominance in the MN blood groups of humans (less famous than the ABO blood groups, but still important!). A person's MN blood type is determined by his or her alleles of a certain gene. An L^ML M allele specifies production of an M marker displayed on the surface of red blood cells, while an L^NL N allele specifies production of a slightly different N marker.