Meiosis & Genetic Diversity (College Board AP® Biology): Study Guide

Meiosis has several mechanisms that increase the genetic diversity of gametes produced which can be advantageous for natural selection

Crossing over is the process by which non-sister chromatids exchange alleles

This process occurs during meiosis I

1. Homologous chromosomes pair up and are close to each other

2. Sections of DNA from non-sister chromatids can cross over and get entangled

3. These crossing points are called chiasmata

4. A section of chromatid from one chromosome may break and rejoin with the chromatid from the other chromosome

This trading of alleles is significant as it can result in a new combination of alleles on the two chromosomes, which increases genetic diversity among the resultant gametes

Independent assortment is another process that increases variation during gamete formation

It involves the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during metaphase I (of meiosis)

In prophase I homologous chromosomes pair up and in metaphase I they are pulled towards the equator of the spindle

• The process is random

• Each pair can be arranged with either chromosome on top

• The orientation of one homologous pair is unaffected by the orientation of any other pair

The homologous chromosomes are then separated and pulled apart to different poles

The combination of alleles that end up in each daughter cell depends on how the pairs of homologous chromosomes were lined up

Each gamete carries substantially different alleles

During fertilization, any male gamete can fuse with any female gamete to form a zygote

This random fusion of gametes at fertilization creates genetic variation between zygotes as each will have a unique combination of alleles

The presence of genetically diverse zygotes contributes to the genetic diversity of a species