a mole has two alleles for fur color, b = brown fur and b = white fur. in a population of 100 moles, 12 have white fur.  a) what is the brown fur allele frequency?   b) the mole  population is at hardy-weinberg equilibrium. how does the gene pool of the population change over time?  

I'll assume is completely dominant over . Recall the Hardy-Weinberg equations:



where represents the allele frequency for brown fur, or the number of copies of the allele within the population; and represents the allele frequency for white fur, or the number of copies of . In the first equation, the squared terms refer to the frequencies of the corresponding homozygous individuals, while is the frequency of the heterozygotes.

We're told that 12 individual moles have white fur, so we know for sure that there are 12 homozygous recessive individuals, which means



from which it follows that



Over time, H-W equilibrium guarantees that the allele frequencies do not change within the population. For example, suppose we denote the frequency of the allele in generation by . Then



That is, the frequency in the -th generation has to match the frequency of attributed to the and half the individuals of the previous generation.



The same goes for .