Meiosis

Meiosis

• Similar in many ways to mitosis
• Several differences
• Involves 2 cell divisions
• Results in 4 cells with 1/2 the normal genetic information.

• Vocabulary:

• Diploid (2N) - Normal amount of genetic material
• Haploid (N) - 1/2 the genetic material.

• Meiosis results in the formation of haploid cells.
• In Humans, these are the Ova (egg) and sperm.
• Ova are produced in the ovaries in females
• Process is called oogenesis
• Sperm are produced in the testes of males.
• Process is called spermatogenesis

Spermatogenesis & Oogenesis

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• Meiosis occurs in 2 phases; Meiosis I, & Meiosis II.

• Meiosis I.
• Prior to division, amount of DNA doubles

 

• During metaphase 1 homologous chromosomes line-up along the metaphase plate
• Areas of homologous chromosomes connect at areas called chiasmata

• Crossing Over of genes occurs now.

• Segments of homologous chromosomes break and reform at similar locations.
• Results in new genetic combinations of offspring.
• This is the main advantage of sexual reproduction

 

• During anaphase 1, each homologous chromosome is pulled to opposite sides of the cell. Unlike mitosis, THE CENTROMERES DO NOT BREAK.

• Nuclei may or may not reform following division.
• Cytokenesis may or may not occur.

• Meiosis II.

• DNA does not double
• Chromosomes randomly line-up along metaphase plate like regular mitosis.
• During anaphase 2, CENTROMERES BREAK and each chromosome is pulled to opposite sides of the cell.

• Nuclei reform and cytokenesis usually occurs (although it is often unequal).