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