c-13 part ii non-mendelian inheritance most phenotypes reflect the influences of several to many...
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C-13 Part IINon-Mendelian inheritance
Most phenotypes reflect the influences of several to many genes
and by the environment
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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
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Pleiotropic effects
• Occurs when an allele has >1 effect on phenotype
• Examples are:– Sickle cell anemia
– Cystic fibrosis
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Incomplete dominance
• Situation where 2 alleles “blend” to form hybridized phenotype
• Examples:– Flower color in 4
o’clocks and snapdragons
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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
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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
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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)
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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
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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-