Meiosis Prepared by Nouf khalid ALSultan Meiosis Division

Meiosis Prepared by: Nouf khalid AL-Sultan

Meiosis Division It’s includes 2 successive nuclear divisions. Meiosis ׀ During which homologous chromosomes separate. Meiosis װ During which sister chromatids of each chromosome separate.

The Stages of Meiosis 1 1 - The homologous chromosomes pair together (4 chromatids). 2 - The aligned chromatids of the 2 chromosomes interchange segments in a process called crossing-over. 1(1) Prophase 1

Crossing Over The exchange of genetic material between homologues occurs during prophase of Meiosis 1. Occurs when homologous portions of two non-sister chromatids trade places.

Crossing Over

2(1) * Homologous chromosomes pairs of line up in the equatorial plane. Metaphase 1 * Homologous chromosomes separate , each chromosome (consisting of 2 sister chromatids). 3(1) Anaphase 1

* Homologous chromosomes have reached the opposite poles where only hal. F (haploid=1 N)chromosomes can be seen. 4(1) Meiosis 2 1(2) Telophase 1 * The chromosomes condense fully again. * The nuclear envelope breaks * It is not preceded by DNA replication. Prophase 2

2(2) 3(2) Metaphase 2 Anaphase 2 *Sister chromatids separate as the centromeres split up. * Each chromatid now is a chromosome.

4(2) Telophase 2 *Division is complete Four haploid daughter cells are formed. * The chromosomes disperse into chromatin threads.

Magnification power 4 x Magnification power 40 x Meiosis 1 Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Meiosis 2 Prophase 2 Metaphase 2 Anaphase 2 Telophase 2

Prophase I Anaphase I Meiosis - I Metaphase I Telophase I

Meiosis - II Prophase II Metaphase II

Meiosis - II Anaphase II Telophase II

COMPARISON MITOSIS and MEIOSIS Mitosis: Meiosis: – Occurs in somatic (body) cells. – Occurs in germ cells (immature reproductive cells) – Growth, development, replacement & repair. – Production of gametes (sex cells) – Produces 2 daughter cells. – Produce 4 daughter cells. – Daughter cells are diploid (2 N). – Daughter cells are haploid (1 N).