Meiosis

Gamete ProductionGamete Production

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MeiosisMeiosisSimilarSimilar in many ways to in many ways to mitosismitosis

Several differences howeverSeveral differences howeverInvolves Involves 2 cell divisions2 cell divisionsResults in Results in 4 cells 4 cells with with 1/2 the 1/2 the normal genetic information.normal genetic information.

Vocabulary:Vocabulary:Diploid (2N) Diploid (2N) - Normal amount - Normal amount of genetic materialof genetic material

Haploid (N)Haploid (N) - 1/2 the genetic - 1/2 the genetic material.material.

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MeiosisMeiosisMeiosis results in the Meiosis results in the formation of formation of

haploid cellshaploid 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 in femalesfemales

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

Process is called Process is called spermatogenesisspermatogenesisMeiosis occurs in 2 phases: Meiosis occurs in 2 phases: Meiosis IMeiosis I

& & Meiosis IIMeiosis II

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Spermatogenesis & Spermatogenesis & OogenesisOogenesis

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Sperm Sperm formatiformati

onon

Egg Egg formatiformati

onon

Meiosis IMeiosis IPrior to division (Prior to division (S phaseS phase), amount of ), amount of DNA doublesDNA doubles

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Metaphase IMetaphase IDuring Metaphase Metaphase

II homologous homologous chromosomes chromosomes line-up along the metaphase plate or EQUATOREQUATOR

Areas of homologous chromosomes connectconnect at areas called CHIASMATACHIASMATA

Genes are Genes are exchanged at exchanged at these these connectionsconnections

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Crossing OverCrossing OverSegments of Segments of

homologous homologous chromosomes chromosomes breakbreak and reattach and reattach at similar at similar locations.locations.

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

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

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Anaphase IAnaphase IDuring Anaphase I, each During Anaphase I, each

HOMOLOGOUS HOMOLOGOUS CHROMOSOMECHROMOSOME is pulled is pulled to opposite sides of the to opposite sides of the cell.cell.

Unlike mitosis, the Unlike mitosis, the CENTROMERES DO NOT CENTROMERES DO NOT BREAKBREAK..

Nuclei MAY OR MAY NOT Nuclei MAY OR MAY NOT reform following division.reform following division.

CYTOKENESISCYTOKENESIS may or may or may not occur.may not occur.

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Meiosis IIMeiosis IIDNA DNA DOES NOT DOES NOT doubledoubleChromosomes randomly line-Chromosomes randomly line-

up along metaphase plate like up along metaphase plate like regular mitosis.regular mitosis.

During During Anaphase II, Anaphase II, CENTROMERES BREAK CENTROMERES BREAK and and each each SISTER CHROMATID SISTER CHROMATID is is pulled to opposite sides of the pulled to opposite sides of the cell.cell.

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

Sister chromatids10

Overview of MeiosisOverview of Meiosis

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