who can explain the relationship between population size and genotype and allele frequency?

Well I for sure can't!

1. One requirement for the Hardy-Weinberg principal to apply to a population is that it must be extremely large. In a large populaton, changes in genotype will not completely alter the allele frequencies. However in smaller populations, a change in the genotype can dramatically change the alle frequencies. For example, in a population of 1000 flowers, there are 500 blue ones and 500 red ones. In the next generation, if there are 480 blue ones and 520 red ones then the allele frequency has not really changed. However in a population of 10 flowers, if 5 were blue and 5 were red, then a change in genotypes in the next generation would fluctuate the allele frequency dramatically.

2. It is neccessary to get an appropriate sample size of the population  in order to get an accurate portrayal of the population. A sample size that is too small might leave out some genotypes or might contain too much of a genotype that is not really common too the population. An appropriate sample size of the population will include an accurate representation of the allele frequencies in the population.

3. The Hardy-Weinberg equation, p2 + 2pq + q2, approximates what percentage of the population are homozygous dominant, heterozygous and homozygous recessive.