5.2 Meiosis & Genetic Diversity

Shuffling the genes

Meiosis generates enormous genetic diversity through two main mechanisms. Crossing over happens in prophase I, when homologous chromosomes exchange segments, mixing alleles. Independent assortment happens at metaphase I, when homolog pairs line up in random orientations.

One more source

Beyond meiosis, random fertilization — any sperm meeting any egg — multiplies the variation even further. Together these create the genetic recombination that makes each offspring unique and gives natural selection variation to act on.

Key terms

Crossing over

Exchange of segments between homologous chromosomes during prophase I.

Independent assortment

Random orientation of homolog pairs at metaphase I, shuffling chromosomes into gametes.

Genetic recombination

New combinations of alleles produced by crossing over and independent assortment.

Random fertilization

Any sperm fertilizing any egg, adding further genetic variation.

Source of variation

Meiosis (crossing over, assortment) plus random fertilization.

Try an AP-style question

An organism has a diploid number of 2n = 6. Ignoring crossing over, how many different combinations of chromosomes can its gametes have?

1. 64
2. 6
3. 8
4. 3