meiosis

• Meiosis only takes place in sex organs and is only used to produce gametes
• gametes in animals are sperm and egg cells
• gametes in plants are pollen and ovules
• meiosis produces 4 haploid daughter cells (n) with half the number of chromosomes as diploid parent cell (2n)
• all gametes produced by meiosis are genetically different
• Homologous` pairs of chromosomes are the same size and shape with the same genes but can contain different alleles
• crossing over happens when homologous chromosomes exchange genetic material at chiasmata
• There are two mechanisms in meiosis independent assortment and crossing over
• Independent assortment means the proportion of maternal or paternal chromosomes that end up on each side of the equator is due to chance and is completely random
• Independent assortment occurs in metaphase 1 and increases genetic diversity
• Chiasma is formed between non-sister chromatids from adjacent regions of the chromosomes
• Crossing over occurs during prophase 1 where homologous chromosome pairs line up along the length of the cell
• in Meiosis there are two rounds of division meiosis 1 and meiosis 2
• Meiosis 1 produces four haploid cells with different combinations of genes
• In meiosis 2 sister chromatids separate so each daughter cell has one copy of each gene
• During prophase 1 DNA condenses and becomes visible homologous chromosomes linked together forming chiasmata or bivalents and the nuclear membrane breaks down and centrioles move to opposite poles of the cell
• during metaphase 1 pairs of Homologous chromosomes are lined up on the equator of spindle apparatus
• during anaphase 1 spindle fibres shorten and Homologous chromosomes move to opposite poles
• during telophase 1 nuclear membrane reforms at either pole of the cell and chromosome uncoils into chromatin state cell also goes under cytokinesis at this point
• during cytokinesis the cytoplasm divides by constriction forming two new cells