Definitions
Allelic Frequency is the number of a specific allele over the total number of alleles.
Individual Frequency is the number of individuals with a trait divided by the total number of individuals.

Example
People with type dominant trait p is 84% while 16% of the people have the recessive q. Find the allelic frequency and the frequency of individuals that are homozygous dominant and heterozygotes (or carriers).

Suggested Method
A. Always use the recessive trait to find the allelic frequency!
The frequency of trait q is 0.16.
To find the frequency of the allele you need to take the square root.
Therefore the allelic frequency is 0.4.

B.  The dominant + recessive frequencies = 1   (p + q = 1).
Since the frequency of the recessive allele is 0.4, it must be subtracted from 1.

p + 0.4 = 1

p = 1 - 0.4

p = 0.6

C.  Determine the individual frequencies using p² + 2 pq + q² = 1.

Genotype	Designation	Frequency	Percent
Homozygous Dominant	pp or p2	(0.6)2 = 0.36	36%
Heterozygote	pq	2(0.4)(0.6) = 0.48	48%
Homozygous Recessive	qq	(0.4)2 = 0.16	16%

 
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Practice Problems:

1.    Seventy percent of a population have the dominant trait while 30% are recessive.  What percentage of the population are carriers? Answer
 

2.    It is determined in a certain population that 1% of the people do not have freckles.  What percentage of the population are carriers for this trait? Answer
 

3.    Pea seeds can be round (R: dominant) or wrinkled (r: recessive). In a field of wild peas ninety-six percent (96%) of the peas are round.  What is the allelic frequencies? Answer
 

4.    For foxes there exists a single gene that controls coat thickness.  Allele C confers a thick coat while allele c a thin coat. In a certain population of 540 foxes, 49 have a thin coat. What are the allelic and individual frequencies? Answer
 

5.    In a certain population of flowers, when red and white flowers are crossed they produce pink flowers.  A certain field has 1190 red flowers, 1070 pink flowers and 240 white flowers.  What is the frequency of individuals and alleles? Answer
 

6.  One person in 10,000 has PKU which is a potentially lethal, recessive disorder. These individuals lack an enzyme  that allows the digestion of the amino acid phenylalanine and must be careful not have this amino acid in their diet.  What are the chances that someone is a carrier, their spouse is a carrier and then their child being a PKU victim?   Answer
 
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