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1.
In a B130 class, 20% of the students have dimpled chins (a dominant trait), whereas 80%
have nondimpled chins. (note: the square root of 0.20 = 0.45, the square root of 0.80 = 0.89)
What is the frequency of the recessive allele in this population? What is the frequency of the
dominant allele in this population? Please show your work.
Since we have 80% recessive phenotype (nondimpled chins), we take the square root of 0.80 to
get 0.89. Thus the frequency of nondimpled chins would be 89% in the population. Allele
frequencies will always be: p + q = 1, so since q (recessive) is 0.89, we take 1  0.89 which gives
0.11, which is the frequency of dimpled chins. So, 89% is the frequency of nondimpled chins,
and 11% is the frequency of dimpled chins. (The homozygous genotype frequencies (p^2 and
q^2) are the squares of the allele frequencies, so that is why we need to take the square root)
2.
Genetic drift: A) refers to random changes in gene frequency in a population B) can be
brought about by a population bottleneck C) occurs through selective forces in the environment
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 Fall '07
 Nesmith
 Biology

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