1. Mutation: This is the ultimate source of new genetic variation. Mutations are changes in the DNA sequence. These changes can be caused by environmental factors (like radiation) or by errors during DNA replication. Mutations can be beneficial, harmful, or neutral in their effects.

2. Recombination: This refers to the shuffling of existing genetic material during sexual reproduction. During meiosis, chromosomes exchange genetic information, leading to new combinations of alleles in offspring. This process is crucial for generating diversity within populations.

3. Gene Flow: This involves the movement of genes between populations. When individuals migrate from one population to another, they introduce new alleles into the receiving population. This can increase genetic diversity in the recipient population, especially if it is small and isolated.

These three sources of genetic variation are constantly working together to generate the incredible diversity we see in the living world.