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I). Meiosis basics
A). Cell division that results in the creation of haploid gametes.
B). Meiosis occurs during:
Gametogenesis: formation of gametes
Somatic cells are 2n. They contain a set of chromosomes one from the mother one from the father
One pair of chromosomes
Each contain only one member of each homologue pair.
When fertilization occurs the normal diploid number is returned.
D). Meiosis involves 2 separate cell divisions and produces 4 daughter cells
II). Stages of Meiosis
A). Meiosis I (Duplication & Crossing over)
1). Interphase I
- DNA replicates
2). Prophase I
|Chromatids coil and condense|
|Synapsis and crossing over occurs|
i). STEP i: Homologues chromosomes form tetrads
ii). STEP ii: The arms chromosomes wrap around each other.
iii). STEP iii: The arms of the homologues crossover.
Advantage: increased variability in the offspring.
3). Metaphase I
Line up on the equator.
4). Anaphase I
Separate but centromeres do not break.
5). Telophase I
a). Daughter cells have haploid chromosome number because they do not have homologues chromosomes.
They have either the maternal or the paternal part of the pair. It varies for each pair.
b). Daughter cells have diploid DNA material because the sister or duplicate chromatids are still attached.
B). Meiosis II
1). Prophase II
chromosomes do not duplicate
2). Metaphase II
line up on the equator
3). Anaphase II
4). Telophase II & cytokinesis
The nuclear envelope begins to form and cytokinesis occurs.
5). 4 haploid daughter cells
& 1 ovum
3 polar bodies