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Example1 - The Punnett square above can be summarized as...

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Example: 3 loci (polygenic) Height (tallness) in humans is polygenic but the mechanism of gene function or the number of genes involved is unknown. Suppose that there are 3 loci with 2 alleles per locus (A, a, B, b, C, c). Assume that: Each active allele (upper case letters: A, B, or C) adds 3 inches of height. The effect of each active allele is equal, A = B = C. Males (aabbcc) are 5' tall. Females (aabbcc) are 4'7". Genotype Males Females aabbcc 5'0" 4'7" Aabbcc (or aaBbcc etc.) 5'3" 4'10" AaBbcc etc. 5'6" 5'1" AaBbCc etc. 5'9" 5'4" AaBbCC etc. 6'0" 5'7" AaBBCC etc. 6'3" 5'10" AABBCC 6'6" 6'1" The following is a cross between two people of intermediate height. AaBbCc X AaBbCc If there is independent assortment, the following gametes will be produced in equal numbers: ABC, ABc, AbC, aBC, abC, aBc, Abc, abc Punnett square analysis:

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Unformatted text preview: The Punnett square above can be summarized as follows: Genotype Males Females Frequency AABBCC 6'6" 6'1" 1/64 AaBBCC etc. 6'3" 5'10" 6/64 AaBbCC etc. 6'0" 5'7" 15/64 AaBbCc etc. 5'9" 5'4" 20/64 AaBbcc etc. 5'6" 5'1" 15/64 Aabbcc etc. 5'3" 4'10" 6/64 aabbcc 5'0" 4'7" 1/64 The frequency column in the table above can be plotted to produce the graph below. Variability Variability results in a bell-shaped curve (see the diagram above). Traits with many loci produce many categories. In the example above, 3 loci produced 7 possible heights because a person could have anywhere from 0 to 6 active alleles. If a trait were determined by 4 loci (AABBCCDD for example) there would be 9 possible categories because a person could have anywhere from 0 to 8 active alleles....
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