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Understanding Non-Mendelian Inheritance: Polygenic Traits and Environmental Effects

This article delves into non-Mendelian inheritance patterns, emphasizing the complexity of phenotypes shaped by multiple genes and environmental influences. Key concepts include polygenic traits, where traits like human height and weight show continuous variation. Pleiotropic effects are discussed, as seen in disorders like sickle cell anemia. The impact of incomplete dominance and epistasis on phenotypic expression, such as flower color and animal coat coloration, is further explored. Additionally, the article touches on the role of gene mutations and the inheritance patterns of blood groups.

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Understanding Non-Mendelian Inheritance: Polygenic Traits and Environmental Effects

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  1. C-13 Part IINon-Mendelian inheritance Most phenotypes reflect the influences of several to many genes and by the environment

  2. Continuous variation • When multiple genes act together to produce a physical (phenotypic) character, a gradation or range of differences occur. • Examples: height, weight in humans • Referred to as polygenic traits

  3. Pleiotropic effects • Occurs when an allele has >1 effect on phenotype • Examples are: • Sickle cell anemia • Cystic fibrosis

  4. Incomplete dominance • Situation where 2 alleles “blend” to form hybridized phenotype • Examples: • Flower color in 4 o’clocks and snapdragons

  5. Environmental effects • Allele expression may be affected by environmental conditions • Examples: • Coat color in arctic foxes • Coat color in Himalayan rabbits and Siamese cats • ch allele affected by temp >33 C  tyrosinase enzyme inactivates + reduces melanin pigment production

  6. Epistasis – genes acting “in concert” • Situation whereby 1 gene pair affects the expression of a 2nd gene pair • Examples: • Anthocyanin (purple) pigment in corn • Animal coat colors

  7. Epistasis (cont’d) • Horse coloration involves 2 or more gene pairings.. • EE or Ee is for black • ee is for red (sorrel) • PLUS other genes can add to base colors • (Bay is AA, EE – black with agouti gene; Buckskin is AA, EE, CcrC – bay with cremello gene, Dun is AA, EE, Dd – bay with dun gene; Palomino is ee, CcrC – sorrel with cremello gene)

  8. Mutation of genes causes genetic disorders • Most gene disorders are RARE – nonadaptive • Most are recessively inherited: • Tay Sachs disease Sickle cell anemia • Some disorders are inherited in a dominant fashion: • Huntington’s disease

  9. Multiple alleles and Blood Groups • ABO Blood groups • IAIA and Iai = type A • IBIB and IBi = Type B • IAIB and IBIA = Type AB • ii = Type O • Rh blood factor • Rh + • Rh-

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