MEIOSIS

PMAT x2

Interphase: Duplicated centrisomes- S Phase DNA is copied.

Prophase:   Chromatids shorten and thicken Chromosomes undergo synapses - 2 homologous chromosomes come near eachother  - each has 2 chromatids so 4 chromatids aligned next to each other Crossing over occurs - segments of DNA from one chromatid swapped with another - result in genetically new chromatid Chromatids are now genetically different from original 4 chromatids.

Metaphase: Chromatids align in middle Centromeres attach to spindle fibres Independent orientation - 2^pairs - 2^23=8,388,608 ----> variation

Anaphase: Homologous pairs get seperated. Homologous chromosome=2 chromatids 23 chromosomes move to each pole reduction-division

Telophase Nucleus reorganize & chromosomes become chromatin Cytokinesis takes place 2 cells - 23 chromosomes

MEIOSIS 2:

PROPHASE II: Chromatin material condenses Chromosomes contain 2 chromatids attached by a centromere 23 chromatid pairs move to equatorial plate

METAPHASE II: 23 chromatid pairs gather to centre of cell before seperation Spindle attaches to centromere

ANAPHASE II: Centromeres divide and 46 chromatids become known as 46 chromosomes Spindle fibres move one chromosome from each pair to opposite poles 23 chromosomes move to each pole

TELOPHASE II: Chromosomes gather at poles and mass of chromatin formed Nuclear envelope develops, nucleoli reppears and cytokinesis takes place Each cell contains a single set of chromosomes 4 cells produced.

New Page