Dictionary of Human Evolution and Biology

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Recessive Pattern Of Inheritance

In Mendelian genetics, a system of inheritance in which, when one allele of any ancestral homozygote mutates to form a new heterozygote, the phenotype of that heterozygote is not distinguishable from that of the ancestral homozygote. In this circumstance, the ancestral homozygote is termed the dominant homozygote (AA), and the de novo heterozygote is termed Aa, with the lower-case a used to symbolize the new recessive mutant. In a recessive system, the heterozygote is often called the carrier of the trait, whereas the recessive homozygote (aa) often exhibits subvital phenotypic changes and reduced fitness. An example is pea shape in common garden peas.

See dominant pattern of inheritance, codominant pattern of inheritance, and incomplete dominance.

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