SECTION 11.4Meiosis

A) STAGES OF MEIOSIS

-Final product will be 4 haploid cells-2 stage process

a) Meiosis Ib) Meiosis II

Homologsseparate

Sister chromatidsseparate

Result: one copy of each chromosome in a gamete.

Haploid

Diploid

Meiosis I(reductiondivision)

Meiosis II(equationaldivision)

Haploid

Meiosis: 2 divisions

A) STAGES OF MEIOSIS

Interphase- replicate DNAa) G1b) Sc) G2

A) STAGES OF MEIOSIS

1) Meiosis Ia) Prophase (same as Mitosis w/ extra)

1. Synapsis:2. Crossing over: exchange pieces of

_________ btwn homologous paira) genetic recombination:

exchange of

a) Prophase I a) Prophase I

Early prophase

Homologs pair. Crossing over occurs.

Late prophase

Chromosomes condense.Spindle forms.

Nuclear envelope fragments.

Recombination Recombination (crossing over)(crossing over)

Occurs in prophase Occurs in prophase of meiosis Iof meiosis I

Generates diversityGenerates diversity

Letters denote genes Case denotes alleles

•Creates chromosomes with new combinations of alleles for genes A to F.

A

B

C

D

E

F

a

b

c

d

e

f

c

d

e

f

A

B

a

b

C

D

E

F

ChiasmatChiasmata a

Crossing overCrossing over

or recombinationor recombination

events create events create

chiasmata.chiasmata.

b) Metaphase Ib) Metaphase I

1. Homolog pairs alignalong the equator of the cell

2. Sister Chromatids facing opposite poles

Homologs separate andmove to opposite poles.

Sister chromatids remain Attached at their centromeres

c) Anaphase II

A) STAGES OF MEIOSIS

Metaphase I-1. __________ line up in the middle of

the cellAnaphase I-

1. 2. independent assortment: random

separation of homologues = ________________

A) STAGES OF MEIOSIS

d) Telophase I-1. chromosomes reach poles2. _____________ takes place3. 2 new haploid cells created ( 2

copies of chromosomes in each cell)

Telophase ITelophase I

Nuclear envelopes reassemble.

Spindle disappears.

Cytokinesis divides cell into two.

Meiosis I :reduction Meiosis I :reduction divisiondivision

Prophase I(early)

(diploid)

Prophase I(late)

(diploid)

Metaphase I(diploid)

Anaphase I(diploid)

Telophase I(diploid)

Nucleus Spindlefibers

Nuclearenvelope

A) STAGES OF MEIOSIS

2) Meiosis IIa) Prophase II

1. spindle fibers appearb) Metaphase II

1. chromosomes align in middle of cellc) Anaphase II

1. Sister chromatids move toward polesd) Telophase II

1. nuclear envelope appears & cytokinesis takes place

Prophase IIProphase II

Nuclear envelope fragments.

Spindle forms.

Metaphase IIMetaphase II

Chromosomes align along equator of cell.

Anaphase IIAnaphase II

Sister chromatids separateand move to opposite poles.

Telophase IITelophase II

Nuclear envelope assembles.

Chromosomes decondense.

Spindle disappears.

Cytokinesis divides cell into two.

A) STAGES OF MEIOSIS

Results of Meiosis:1) ______ Haploid cells are created2) Contains ______ the # of chromosomes as

original cell3) _________ variation

Mitosis Meiosis

Number of divisions 12

Number of daughter cells

2 4

Genetically identical?

Yes No

Chromosome # Same as parent Half of parent

When Throughout life At sexual maturity

Role Growth and repair Sexual reproduction

B) FORMATION OF GAMETES

1) Animal cell: meiosis occurs in reproductive organs

a) Ex: __________________

2) Spermatogenesis: production of _______3) Oogenesis: production of ________

a) Polar bodies: remaining cells from meiosis

SPERM AND EGG

Oogonium(diploid)

Mitosis

Primaryoocyte(diploid)

Meiosis I

Secondaryoocyte(haploid)

Meiosis II

(if fertilizationoccurs)

First polar bodymay divide (haploid)

Polarbodiesdie

Ovum (egg)

Secondpolar body(haploid)

a

A

X

X

a

X

A X

a

X

a

X

Matureegg

A

X

A

X

C) ASEXUAL AND SEXUAL REPRODUCTION

1) Asexual Reproduction: reproduction of offspring from 1 parent

a) Ex: _____________

2) Sexual Reproduction: reproduction of offspring by a sex cell from each parent