Meiosis

• Homologous chromosomes: a pair of chromosomes, one from each parent.

• Haploid (n): one set of chromosomes

• Diploid (2n): two sets of chromosomes

• n = number of chromosomes

What do we need to know?(background information)

Two major types of cells

• Somatic or body cells-(most of our cells)

examples: skin, stomach, brain, liver, blood cells, etc.

• Sex cells or germcells (also called gametes) ex. Egg and sperm

Within each somatic (body) cell are chromosomes

• Sex Chromosomes:the X and Y that determine the gender of an organism.

males- XYfemales- XX

• Autosomes: all of the other chromosomeschromosomes 1-22

What is Meiosis?• Meiosis makes

germ cells, eggs and sperm

• Meiosis is a cell division process that reduces the number of chromosomes byhalf

• There are two main stages of Meiosis.

Meiosis I

Crossing Over

• During prophase of Meiosis I, the homologous chromosomes form tetrads, which may exchange genetic information. This increases genetic variability and is called crossing over.

Independent Assortment of chromosomes

• The chromosomes line up during metaphase I at random which leads to genetic variability.

Inherited from mother (red)

Inherited from father (blue)

Meiosis II