Below are five causes of genetic variation:
1. Crossing over is the exchange of gene segments between homologous chromosomes. This results in each of the chromosomes having a mixture of parental characteristics in offspring.
2. Mutations are errors in the "normal" DNA sequence. Mutations are how new genetic sequences are formed.
3. Random fertilization refers to the probability of which single male sperm, out of the hundreds of thousands to millions that are released during ejaculation, actually lands on, enters and fertilizes the female egg.
4. Independent assortment refers to the independent separation of each allele for a characteristic during meiosis.
5. Migration is the movement of living things from one area to another. Immigration is the migration into a new location. Immigration is when a living thing exits his/her current location. Migration leads to genetic variation because individuals, who would not have otherwise met, are more apt to mate. This mixes two gene pools from two different populations and results in an increase in variation.