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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