MeiosisMeiosis Similar in many ways to mitosisSimilar in many ways to mitosis Several differences howeverSeveral differences however

Involves 2 cell divisionsInvolves 2 cell divisions Results in 4 cells with 1/2 the normal genetic information.Results in 4 cells with 1/2 the normal genetic information.

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

Meiosis results in the formation of haploid cells.Meiosis results in the formation of haploid cells. In Humans, these are the In Humans, these are the OvaOva (egg) and (egg) and spermsperm.. Ova are produced in the Ova are produced in the ovariesovaries in females in females

Process is called Process is called oogenesisoogenesis Sperm are produced in the Sperm are produced in the testestestes of males. of males.

Process is called Process is called spermatogenesisspermatogenesis Meiosis occurs in 2 phases: Meiosis occurs in 2 phases: Meiosis 1Meiosis 1 & & Meiosis 2Meiosis 2

Spermatogenesis & Oogenesis

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

Metaphase 1Metaphase 1

During metaphase 1 During metaphase 1 homologous homologous chromosomes line-chromosomes line-up along the up along the metaphase platemetaphase plate

Areas of Areas of homologous homologous chromosomes chromosomes connect at areas connect at areas called called chiasmatachiasmata

Crossing OverCrossing Over Segments of Segments of

homologous homologous chromosomes break chromosomes break and reform at similar and reform at similar locations.locations.

Results in new genetic Results in new genetic combinations of combinations of offspring.offspring.

This is the main This is the main advantage of sexual advantage of sexual reproductionreproduction

Anaphase 1Anaphase 1 During anaphase 1, each homologous chromosome is pulled to During anaphase 1, each homologous chromosome is pulled to

opposite sides of the cell. Unlike mitosis, opposite sides of the cell. Unlike mitosis, THE THE CENTROMERES DO NOT BREAKCENTROMERES DO NOT BREAK..

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

Meiosis IIMeiosis II

DNA DNA does notdoes not double double Chromosomes randomly line-up along metaphase Chromosomes randomly line-up along metaphase

plate like regular mitosis.plate like regular mitosis. During anaphase 2, During anaphase 2, CENTROMERES BREAKCENTROMERES BREAK

and each chromosome is pulled to opposite sides and each chromosome is pulled to opposite sides of the cell.of the cell.

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

Overview of MeiosisOverview of Meiosis