In a population of peppered moths 25 of the population shows

In a population of peppered moths, 25% of the population shows the recessive phenotype of white. Show your work where appropriate. a) which variable does 25% represent? b) what is the frequency of recessive alleles in the population? c) what is the value of p? d) If this population had 1500 moths, how many moths would be homozygous dominant (AA), heterozygous (Aa) and homozygous recessive?

Solution

As 25% of population show recessive phenotye of white.

a. The variable 25% represents aa (Recessive Phenotype)
b. The frequency of aa is 25%, which means that q² = 0.25, by definition. If q² = 0.25, then q = 0.5, again by definition. Since q equals the frequency of the a allele, then the frequency is 50%.
c. Since q = 0.5, and p + q = 1, then p = 0.5
d. Population has 1500 moths and it is already given that 25% are recessive, hence aa=25%
No. of moths with homozygous recessive condition (aa) = 25% of Total number of moths
= 25 x1500  
100
= 375 moths

No. of moths with homozygous dominant condition (AA) ( As the frequency of p was calculated earlier, we will work with that value, p=0.5 , therefore, p² = 0.5x0.5 =0.25 . The frequency of AA is 25%.

So, as in earlier step, the no. of moths with homozygous dominant condition are 25% of total no. of moths = 375 moths.

No. of moths with heterozygous confition (Aa) = Total no. of moths - ( No. of homozygous dominant+ No. of homozygous recessive moths)
= 1500 - (375+375)
= 750 moths

No. of homozygous recessive moths = 375
No. of homozygous dominant moths = 375
No. of heterozygous moths = 750