Sex
Each individual has two homologous copies of each chromosome, one from mom, one from dad.
Sperm/egg have only one copy of each chromosome, chosen randomly.
Homologous chromosomes ‘cross over’ in at least two places during meiosis, further shuffling genes.
Cross over rates are used to make genetic maps. Cross over is different in sperm and egg.
Cross-over between different copies of same transposon can cause large duplications, deletions.