A population is a local group of interbreeding organisms belonging to the same species.  Their gene pool indicates all the genes present in that population.

Allelic frequency:
p + q = 1 where p is the frequency of the dominant allele and q is the frequency of the recessive allele.

Genotypic frequency:
p² + 2pq + q² =1 or (p + q)² = 1 where p² is the frequency of dominant homozygosity, 2pq is the frequency of heterozygosity and q² is the frequency of recessive homozygosity.

What circumstances make these statements true.
.

1. a large population (no genetic drift)
2. isolation of the population (no gene flow)
3. no mutation
4. random mating
5. no natural selection

Example problem:

You observe 167 moths.  You know that white is homozygous dominant, gray is heterozygotic, and black is homozygotic recessive.
a)  if the number of black moths spotted is 12 what is the frequency of both alleles and the three genotypes?

How to do it.

Gene Flow:  allele frequency change in a small population due to chance.
Polymorphism:  a variation within a species; can apply to genes, chromosomes, anatomy, etc.
Genetic drift:  chance change in the allelic frequencies in the gene pool of a small population.

Question:  What causes genetic drift?
Answer:  The creation of small populations by
     a) founder effect
          a few individuals colonize a new area.
     b) bottleneck effect
          a disaster wipes out most of the population.

Try out the Hardy-Weinberg Wizard!

Next:  "Reproduction relative to Evolution."