24genetics3 (1) - Lecture 24: Genetic Inheritance Chapter...

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Lecture 24: Genetic Inheritance Chapter 20: Complex Inheritance Patterns
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The Big Picture Complex Inheritance Patterns
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Polygenic Inheritance Polygenic traits are controlled by many sets of alleles Many genes on many chromosomes Each gene either a dominant or recessive allele
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Polygenic Traits Dominant alleles are cumulative The more dominant alleles you have, the more of the dominant phenotype you observe E.g. skin colour or height
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Continuous Variation Polygenic traits result in a continuous variation of phenotype distribution
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Incomplete Dominance A heterozygote expresses an intermediate form between homozygous dominant and homozygous recessive E.g. wavy hair is in between straight and curly hair
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Incomplete Heterozygous Gene Curly hair: homozygous dominant Straight hair: homozygous recessive Wavy hair: heterozygous If two wavy hair people have children, the expected phenotypic ratio is 1:2:1
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Codominance Alleles are equally expressed in a heterozygous individual Both alleles code for a different product and both products are present E.g. human blood type antigens
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24genetics3 (1) - Lecture 24: Genetic Inheritance Chapter...

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