MEIOSIS: THE PROCESSBiology 12

Cartoon of the day:

Context: Meiosis allows for the formation of sperm and egg cells

Overview: Interphase Meiosis I

Prophase I Metaphase I Anaphase I Telophase I (and cytokinesis)

Meiosis II Prophase II Metaphase II Anaphase II Telophase II (and cytokinesis)

Meiosis I: Interphase The chromatin begins to

condense into chromosomes, which duplicate

Identical to interphase in mitosis

Chromosome duplication

Meiosis I: Prophase I In meiosis (unlike

mitosis), the process called synapsis occurs.

Tetrads of homologous chromosome form

There may be an exchange of genetic material, called crossing over

Crossing over (synapsis): Non-sister chromatids

of homologous chromosomes interchange genes

The pairing (formation of the tetrad) allows crossing over to take place and this enables genetic variations in the daughter cells.

Meiosis I: Metaphase ITetrads line up at the

equatorAlignment is random

so that chromosomes from one will be mixed with the other parent when they move apart

Meiosis I: Anaphase IOne homologous

chromosome of each pair is pulled to each end of the cell.

**Remember in mitosis, it was the chromatids that separated, not pairs of chromosomes!

Meiosis I: Telophase I (and cytokinesis I)

The cell begins to divide into two daughter cells.

Each cell produced after cytokinesis has been reduce from diploid to haploid.

Interphase: Very short DNA is not replicated before meiosis II

Meiosis II: Prophase IINuclear

membrane begins to dissolve

Spindle fibers begin to form

Meiosis II: Metaphase II Spindle fibres attach

to centromeres Sister chromatids

line up at equator

Meiosis II: Anaphase II Centromeres divide

in two Spindle fibres pull

sister chromatids towards opposite ends of cell (pole)

Meiosis II: Telophase II and (cytokinesis II)

Nuclear membrane reforms and cytoplasm divides

Result: Formation of four

cells Are sex cells (egg

or sperm) Haploid (carries

half the number of chromosomes of somatic cells)

Videos: http://www.youtube.com/watch?v=kVMb

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To do: Meiosis colouring sheet Read pages 103-107

Page 107 # 1, 2, 3, 4, 5, 6