Biological variation

Increase variability	Reduce variability
Epigenetic mechanisms Alternative splicing
Recombination
Add alleles	Reduce alleles
Horizontal Gene Transfer Endosymbiotic Gene Transfer
Natural selection	Natural selection
Gene flow	Genetic drift Bottleneck Founder effect
Mutation : Gene: substitutions, insertions and deletions (indels), re-arrangement: point-mutations (SNPs) or multiple bases Chromosome: translocation, inversion, deletion, duplication, non-disjunction