Population genetics(pop-gen):

Study of how population of a species change genetically over time leading to evolution

Group of individuals of a species that can interbreed is called population

Allele frequency:

How often certain alleles turn up in a population.

There are 5 factors which change this

1.Natural selection:

Alleles for fitter organisms become more frequent.

2.Sexual selection:

Alleles for more sexually attractive organisms become more frequent

3.Mutation:

New alleles popping up due to mistakes in DNA copying

4.Genetic drift:

Changes in allele frequency due to random chance
More impactful in small populations

5.Gene flow:

Changes in allele frequency due to mixing with new genetically different populations
More impactful in smaller populations

Hardey-Weinberg principal:

Frequency of alleles remains constant in a population from generation to generation giving that there is:

1. No natural selection
2. No sexual selection
3. No mutation
4. Huge population
5. No gene flow

For mendelian traits,
Let the frequency of a dominant allele be p and the recessive allele be q,
p+q = 1 and p^2 + 2pq + q^2 = 1
p^2 gives the frequency of homozygous dominant
2pq gives the frequency of heterozygous dominant
q^2 gives the frequency of recessive