Fig. 9-1b, p.138

Fig. 9-1c, p.138

Flowering plant

Fig. 9-3a, p.140

anther (wheresexual sporesthat give rise tosperm form)

ovules inside anovary (where sexualspores that giveto eggs form)

Fig. 9-3b-c, p.140

testis(where sperm originate)

Human male Human female

ovary(where eggsdevelop)

one chromatid

its sister chromatid

centromere

one chromosome in the duplicated state

p.141a

p.141b

p.141c

then the partners separate.

Each homologue in thecell pairs with its partner,

one chromosome (duplicated)

two chromosomes (unduplicated)

p.141d

Fig. 9-5a, p.142

plasma membrane

spindle equator (midway between the two poles)

one pair of homologous chromosomes

Prophase I Metaphase I Anaphase I Telophase I

Meiosis I

Fig. 9-5a, p.142

newly formingmicrotubules ofthe spindle

breakupof nuclearenvelope

centrosome witha pair of centrioles,moving to oppositesides of nucleus

Chromosomes were duplicated earlier, ininterphase.

Prior to metaphase I, one set of microtubules had tethered one chromosome of each type to one spindle pole and another set tethered its homologue to the other spindle pole.

One of each duplicatedchromosome, maternal or paternal, moves to a spindle pole; its homologue moves to the opposite pole.

One of each typeof chromosome hasarrived at a spindlepole. In most species,the cytoplasm dividesat this time.

Fig. 9-5b, p.142

Prophase II Metaphase II Anaphase II Telophase II

Meiosis II

there is no DNA replication between the two divisions

Fig. 9-5b, p.142

In each cell, one of two centrioles moves to the opposite side of thecell, and a new bipolar spindle forms.

By now, microtubules fromboth spindle poles have finished a tug-of-war.

The sister chromatids of each chromosome move apart and are now individual, unduplicated

A new nuclear envelopeencloses each parcel ofchromosomes, so thereare now four nuclei.

Fig. 9-6, p.144

a A maternal chromosome (purple) and paternal chromosome (blue) were duplicated earlier, duringinterphase. They become visible in microscopes early in prophase I, when hey star to condense tothreadlike form.

b Each chromosome and its homologous partner zippertogether, so all four chromatidsare tightly aligned.

mom’salleleB

mom’salleleA

mom’salleleA

mom’salleleA

mom’salleleB

dad’sallele

a

dad’salleleb

dad’salleleb

c Here is a simple way to think about crossing over. (Chromosomes are still condensed and threadlike,and each is tightly aligned with its homologous partner.)

d Their intimate contactpromotes crossing over at different places along the length of nonsister chromatids.

e At the crossover site, paternal and maternal chromatids exchangecorresponding segments.

f Crossing over mixesup maternal and paternalalleles on homologouschromosomes.

Fig. 9-6c, p.144

Fig. 9-6d, p.144

Fig. 9-6e, p.144

Fig. 9-6f, p.144

Fig. 9-8, p.146

a Growth b Meiosis I andcytoplasmic division

c Meiosis II and cytoplasmic division

spermatids (haploid)

secondary spermatocytes

(haploid)

primary spermatocyte

(diploid)

Fig. 9-9, p.147

diploid malegerm cell

sperm (mature,haploid male

gametes)

a Growth b Meiosis I and cytoplasmic division

c Meiosis II and cytoplasmic division

ovum (haploid)

primary oocyte (diploid)

secondary oocyte

(haploid)

first polar body

(haploid)

three polar bodies

(haploid)

Fig. 9-10a, p.147

oogonium(diploidfemale

germ cell)

Fig. 9-10b, p.147

Telophase IProphase I Anaphase IMetaphase I

Fig. 9-11a, p.148

In a diploid (2n) germ cell,duplicated chromosomesnow condense. The bipolarspindle forms and tethers thechromosomes. Crossoversoccur between homologues.

Each maternal chromosomeand its paternal homologueare randomly aligned midwaybetween the two spindlepoles. Either one may getattached to either pole.

Homologouspartnersseparateand moveto oppositepoles.

There are two clustersof chromosomes. Newnuclear envelopes mayform and the cytoplasmmay divide beforemeiosis II begins.

Fig. 9-11b, p.149

In a diploid (2n) body cell, the duplicated chromosomes nowcondense. Bipolar spindle formsand tethers the chromosomes.

All chromosomesaligned at thespindle equator.

Sister chromatids of each chromosomemoved to oppositespindle poles.

Two diploid (2n) nuclei form. After cytoplasmicdivision, there are two diploid body cells.

Prophase Metaphase Anaphase Telophase

Mitosis

Fig. 9-11c, p.149

no interphaseand no DNAreplicationbetween thetwo nucleardivisions

Prophase II Metaphase II Anaphase II Telophase IIAll chromosomes stillduplicated. New spindleforms in each nucleus,tethers chromosomesto spindle poles.

All chromosomesaligned at thespindle equator.

Sister chromatids ofeach chromosomemoved to oppositespindle poles.

Four haploid (n) nucleiform. After cytoplasmicdivision, haploid cellsfunction as gametesor spores.

Fig. 9-11d, p.149

Fig. 9-12, p.150

gametes gametes

germ cell germ cell

each chromosomeduplicated during

interphase

MEIOSIS IIseparation of

sister chromatids

MEIOSIS Iseparation ofhomologues

diploid numberrestored atfertilization

zygote

2n

2n

n