drydecay-
Prophase I
Paternal and maternal chromosomes come together in homologous pairs (chromosomes that share the same structural features) This process is called synapses and each homologus pair is called a bivalent.
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Crossing over -
Chromosomes pair up, shorten and twist around eachother causing tension.
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Chiasmata
Sections that break off and exchange with sections of another chromatid
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Metaphase I
Bivalents arrange themselves at the equator. They lie randomly - this is called independent assortment
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Anaphase I
Chromosomes of the bivalents seperate as the spindle fibres shorten. Each pole receives a random arrangement of chromosomes. Centromeres do not split
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Telophase I
The nuclear membrane might reform and the chromosomes uncoil. Cytokinesis - 2 haploid cells
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Prophase II
Centrioles separate and move to right angles of the old spindles
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Metaphase II
Chromosomes line up at the equator and are attached to the centromere by spindle fibres
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Anaphase II
Centromere splits and spindle fibre shorten pulling chromatids to the poles
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Telophase II
Chromatids lengthen and uncoil. Spindles disintegrate and nuclear envelope reforms. Cytokinesis.
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Significance of Meiosis
Sexual reproduction + genetic variation
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Sources of variation
Crossing over + recombination, independent assortment of chromosomes, random fertilisation of gametes and random mating between organisms of the same species
