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More Genetics & Pedigrees. Incomplete Dominance. Multiple Alleles & Codominance. Additive effect of multiple genes on a single phenotype Results in normal distribution Examples: skin color, height. Polygenic Traits. A gene at one locus alters the expression of a gene at another locus. - PowerPoint PPT Presentation
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Polygenic Traits
• Additive effect of multiple genes on a single phenotype
• Results in normal distribution
• Examples: skin color, height
Epistasis
• A gene at one locus alters the expression of a gene at another locus.
• Example: – Black coat (B) is
dominant to brown (b)– Pigment color (C) is
dominant to no pigment color (c)
Probabilities
Aa aaChild will have recessive trait?
aa
Chance of “a” allele from dad?
1/2
Chance of “a” allele from mom?
2/2 (1)
Total
1/2 x 1 = 1/2
X-linked Recessives: More commonly seen in Males
• Why?• Males only need one recessive
allele to see trait.• E.g. Color-blindness
• XC – 92 % of alleles• Xc – 8 % of alleles
Females Males
92%
8%
(0.92)(0.92) = 85%
2x (0.92)(0.08) = 15%
(0.08)(0.08) = 0.64%
XCXC
XCXc
XcXc
XCyXcy
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