Final answer:
As allele frequencies in a finite population drift due to genetic drift, the frequency of heterozygotes decreases and can ultimately vanish as one allele becomes fixed in the population.
Step-by-step explanation:
As allele frequencies in a finite population drift toward fixation or loss due to genetic drift, the frequency of heterozygotes in the population decreases. Genetic drift occurs when allele frequencies within a population change randomly and can lead to the fixation of one allele, effectively eliminating the other allele.
This can result in a decrease in genetic diversity, as one allele becomes dominant in the gene pool. For example, if we start with a population where allele B and allele b are in equal frequencies (p=q=0.5), and only individuals with allele B reproduce, the next generation will have a higher frequency of allele B (p > 0.5) and a lower frequency of allele b (q < 0.5). If this trend continues, eventually allele B may become fixed, and allele b may be lost from the population.
As the population approaches fixation of one allele, the presence of heterozygous individuals (Bb) becomes less likely, reducing genetic variance.