Birth defects like clubfoot cle palate or neural tube

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Unformatted text preview: Recessive: bb •  Pleiotropy: when one gene affects many different traits. •  Polygenic traits: when one trait is governed by mul9ple genes, which maybe on the same chromosome or on different chromosomes. –  The addi9ve effects of numerous genes on a single phenotype create a con9nuum of possible outcomes. –  Polygenic traits are also most suscep9ble to environmental influences. Dominant: Bb or BB Pleiotropy in humans: Phenylketonuria A disorder that is caused by a deficiency of the enzyme phenylalanine hydroxylase, which is necessary to convert the essen9al amino acid phenylalanine to tyrosine. A defect in the single gene that codes for this enzyme therefore results in the mul9ple phenotypes associated with PKU, including mental retarda9on, eczema, and pigment defects that make affected individuals lighter skinned 3 8/26/13 Polygenic Inheritance in Humans •  Height is controlled by polygenes for skeleton height, but their effect may be affected by malnutri9on, injury, and disease. •  Weight, skin color, and intelligence. •  Birth defects like clubfoot, cle^ palate, or neural tube defects are also the result of mul9ple gene interac9ons. •  Complex diseases and traits have a tendency to have low heritability (tendency to be inherited) compared to single gene disorders (i.e. sickle- cell anemia, cys9c fibrosis, PKU, Hemophelia, many extremely rare gene9c disorders). Selec9on •  Some genes may be subject to selec4on, where individuals with advantages or “adap9ve” traits tend to be more successful than t...
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