SECTION 11 4 Meiosis A STAGES OF MEIOSIS

SECTION 11. 4 Meiosis

A) STAGES OF MEIOSIS -Final product will be 4 haploid cells -2 stage process a) Meiosis I b) Meiosis II

Meiosis: 2 divisions Sister chromatids separate Homologs separate Meiosis I (reduction division) Meiosis II (equational division) Diploid Haploid Result: one copy of each chromosome in a gamete.

A) STAGES OF MEIOSIS Interphase- replicate DNA a) b) c) G 1 S G 2

A) STAGES OF MEIOSIS 1) Meiosis I a) Prophase (same as Mitosis w/ extra) 1. Synapsis: 2. Crossing over: exchange pieces of _____ btwn homologous pair a) genetic recombination: exchange of

a) Prophase I Early prophase Late prophase Homologs pair. Crossing over occurs. Chromosomes condense. Spindle forms. Nuclear envelope fragments.

n Recombination (crossing over) Occurs in prophase of meiosis I a A B b C n Generates diversity Letters denote genes Case denotes alleles D E F A a B c b c d d C D E F e f • Creates chromosomes with new combinations of alleles for genes A to F. e f

Chiasmata Crossing over or recombination events create chiasmata.

b) Metaphase I 1. Homolog pairs align along the equator of the cell 2. Sister Chromatids facing opposite poles

c) Anaphase II Homologs separate and move to opposite poles. Sister chromatids remain Attached at their centromeres

A) STAGES OF MEIOSIS Metaphase I 1. _____ line up in the middle of the cell Anaphase I 1. 2. independent assortment: random separation of homologues = ________

A) STAGES OF MEIOSIS d) Telophase I 1. chromosomes reach poles 2. _______ takes place 3. 2 new haploid cells created ( 2 copies of chromosomes in each cell)

Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two.

Meiosis I : reduction division Spindle fibers Nucleus Prophase I (early) (diploid) Prophase I (late) (diploid) Metaphase I (diploid) Nuclear envelope Anaphase I (diploid) Telophase I (diploid)

A) STAGES OF MEIOSIS 2) Meiosis II a) Prophase II 1. spindle fibers appear b) Metaphase II 1. chromosomes align in middle of cell c) Anaphase II 1. Sister chromatids move toward poles d) Telophase II 1. nuclear envelope appears & cytokinesis takes place

Prophase II Nuclear envelope fragments. Spindle forms.

Metaphase II Chromosomes align along equator of cell.

Anaphase II Sister chromatids separate and move to opposite poles.

Telophase II Nuclear envelope assembles. Chromosomes decondense. Spindle disappears. Cytokinesis divides cell into two.

A) STAGES OF MEIOSIS Results of Meiosis: 1) ______ Haploid cells are created 2) Contains ______ the # of chromosomes as original cell 3) _____ variation

Mitosis Meiosis 2 Number of divisions 1 Number of daughter cells 2 4 Yes No Chromosome # Same as parent Half of parent When Throughout life At sexual maturity Role Growth and repair Sexual reproduction Genetically identical?

B) FORMATION OF GAMETES 1) Animal cell: meiosis occurs in reproductive organs a) Ex: _________ 2) 3) Spermatogenesis: production of _______ Oogenesis: production of ____ a) Polar bodies: remaining cells from meiosis

SPERM AND EGG

First polar body may divide (haploid) a a X a Mitosis Oogonium (diploid) A X X Meiosis I X Primary oocyte (diploid) Polar bodies die Meiosis II (if fertilization occurs) A X Secondary oocyte (haploid) Ovum (egg) A X Second polar body (haploid) Mature egg

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