Question of the Day1. Where do humans do meiosis?

2. Why do humans do meiosis?

1. In the testicles and ovaries

2. To ensure genetic variation

Fig. 13-8

Prophase I Metaphase I Anaphase ITelophase I and

CytokinesisProphase II Metaphase II Anaphase II Telophase II and

Cytokinesis

Centrosome(with centriole pair)

Sisterchromatids Chiasmata

Spindle

Homologouschromosomes

Fragmentsof nuclearenvelope

Centromere(with kinetochore)

Metaphaseplate

Microtubuleattached tokinetochore

Sister chromatidsremain attached

Homologouschromosomesseparate

Cleavagefurrow

Sister chromatidsseparate Haploid daughter cells

forming

Metaphase I

Fig. 13-8a

Prophase I Anaphase I Telophase I andCytokinesis

Centrosome(with centriole pair)

Sisterchromatids Chiasmata

Spindle

Homologouschromosomes

Fragmentsof nuclearenvelope

Centromere(with kinetochore)

Metaphaseplate

Microtubuleattached tokinetochore

Sister chromatidsremain attached

Homologouschromosomesseparate

Cleavagefurrow

Fig. 13-8b

Prophase I Metaphase I

Spindle apparatus

Sisterchromatids Chiasmata

Spindle

Genetically differentchromatids

Metaphaseplate

Tetrad withCrossingover Fragments

of nuclearenvelope

Spindle Fiberattached tokinetochore

Fig. 13-8c

Anaphase ITelophase I and

Cytokinesis

Sister chromatidsremain attached

Homologouschromosomesseparate

Cleavagefurrow

Fig. 13-8d

Prophase II Metaphase II Anaphase II Telophase II andCytokinesis

Sister chromatidsseparate Haploid daughter cells

forming

Fig. 13-8e

Prophase II Metaphase II

New spindle fibers form

Sister chromatids positioned on metaphase plate

Fig. 13-8f

Anaphase IITelephase II and

Cytokinesis

Sister chromatidsseparate Haploid daughter cells

forming

Fig. 13-8

Prophase I Metaphase I Anaphase ITelophase I and

CytokinesisProphase II Metaphase II Anaphase II Telophase II and

Cytokinesis

Centrosome(with centriole pair)

Sisterchromatids Chiasmata

Spindle

Homologouschromosomes

Fragmentsof nuclearenvelope

Centromere(with kinetochore)

Metaphaseplate

Microtubuleattached tokinetochore

Sister chromatidsremain attached

Homologouschromosomesseparate

Cleavagefurrow

Sister chromatidsseparate Haploid daughter cells

forming

Fig. 13-9a

MITOSIS MEIOSIS

MEIOSIS I

Prophase IChromosome

replicationChromosome

replication

2n = 6

Parent cell

Prophase

Metaphase Metaphase I

Anaphase ITelophase I

MEIOSIS II

Daughter cells of meiosis II

nnnn

2n2n

Daughter cellsof mitosis

AnaphaseTelophase

Fig. 13-9b

SUMMARY

MeiosisMitosisProperty

DNAreplication

Number ofdivisions

Occurs during interphase beforemitosis begins

One, including prophase, metaphase,anaphase, and telophase

Genetic variation

Does not occur

Number ofdaughter cells

Two, each diploid (2n) and geneticallyidentical to the parent cell

Role in theanimal body

Enables multicellular adult to arise from zygote; produces cells for growth, repair, and, in some species, asexual reproduction

Occurs during interphase before meiosis I begins

Two, each including prophase, metaphase, anaphase, and telophase

Occurs during prophase I along with crossing overbetween nonsister chromatids; resulting chiasmatahold pairs together due to sister chromatid cohesion

Four, each haploid (n), containing half as many Chromosomes as the parent cell; genetically different from the parent cell and from each other

Produces gametes; reduces number of chromosomes by half and introduces genetic variability among the gametes