MeiosisMr. Colosi’s Biology Class

DefinitionThe successful division of a diploid (2N) eukaryotic cell that results in four haploid (N) progeny cells (the gametes in animals).

Each resulting cell has half the genetic material of the original call.

Occurs only in sexually reproducing organisms

Meiosis I and Meiosis IITwo cell divisions take place during meiosis.

In meiosis I, one diploid parent cell divides into two haploid cells (each chromose contains two chromatids).

In meiosis II, the two haploid cells divide into four haploid cells (each chromosome contains one chromatid).

Steps of Meiosis IProphase I Chromatin condenses into chromosomes. Chromosomes are made up of a pair of chromatids. Homologous chromosomes pair up Crossing-over occurs in this step

Metaphase I Chromosomes line up at the middle (equator) of the cell. Microtubules attach to the center of each chromosome.

Anaphase I Microtubules pull the pairs of homologous chromosomes

apart.

Telophase I Cell splits into two daughter cells

Steps of Meiosis IIProphase II, Metaphase II, Anaphase II, & Telophase II Follow the same steps as meiosis I At the end of telophase II, there are four haploid cells. These

cells are the gametes.

Genetic Diversity

When the chromosomes (maternal and paternal) are segregating, crossing-over takes place.

This is what creates the genetic variation that makes everyone different.

Meiosis Videohttp://www.youtube.com/watch?v=D1_-mQS_FZ0

ResourcesCrossing Over. Retrieved from http://www.phschool.com/science/biology_place/labbench/lab3/crossovr.html

Meiosis. Retrieved from http://alenamedina.synthasite.com/meiosis.php

Meiosis. Retrieved fromhttp://www.phschool.com/science/biolo gy_place/biocoach/meiosis/overview.html

Meiosis. Retrieved from http://www.youtube.com/watch?v=D1_-mQS_FZ0

The Phases of Meiosis. Retrieved from http://www.brown.edu/Courses/BI0032/gentherp/phaseIBl1.htm