BSC 114 Lecture Notes - Lecture 21: Epistasis, Mendelian Inheritance, Abo Blood Group System
24 Mar 2016
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Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical (e. g. flower color in pea plants) In incomplete dominance, the phenotype of f1 hybrids is somewhere between the phenotypes of the two parental varieties (e. g. flower color in carnations) In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways. Dominant alleles are not necessarily more common in populations than recessive alleles. For example, one baby out of 400 in the us is born with extra fingers or toes, a condition called polydactyly or polydactylism. The allele for this unusual trait is actually dominant to the allele for the more common trait of five digits per appendage. Most genes have multiple phenotypic effects, a property called pleiotropy. For example, pleiotropic alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease. Some traits may be determined by two or more genes.
