Meiosis

Section 4.3

Gametes

• Cells that contain half the normal number of chromosomes

• 1 chromosome from a parent• Found in the sex organs • Sperm (male), egg (female)

Fertilization

• Union of sperm and egg to form a new cell

Meiosis

• A kind of division that produces gametes with half the number of chromosomes (haploid)

• Makes sure that the correct number of chromosomes will be in the resulting cell (diploid)

• Only takes place in the reproductive tissues of organisms

Steps of Meiosis

• Cells replicate DNA• Prophase I – chromosomes pair up• Metaphase I – chromosomes line up in

middle• Anaphase I – two chromosome copies are

pulled apart• Telophase I and Cytokinesis – cell membrane

forms creating 2 daughter cells

Steps of Meiosis

• Prophase II – homolog copies are attached (no duplication)

• Metaphase II – chromosomes line up in middle

• Anaphase II – copies are pulled apart• Telophase II and Cytokinesis – cell membrane forms creating 4 haploid cells

Meiosis

• Only for cells that are to become gametes• Cell divides twice but only replicates DNA

once

Meiosis

• Daughter cells in meiosis are haploid and have half the normal number of chromosomes

• Daughter cells in mitosis are diploid and contain exactly the same genetic information as the parent

What is happening?