3.30: Understand that Division of a Cell by Meiosis Produces Four Cells, Each with Half the Number of Chromosomes, and that this Results in the Formation of Genetically Different Haploid Gametes

MEIOSIS: Type of cell division that produces four haploid cells that are not genetically identical

FUNCTION:

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• Humans are composed of diploid cells, possessing two copies of each chromosome (one of Maternal origin, one of Paternal origin)
• Hence, for Humans to reproduce, Haploid gametes are needed that contain only one copy of each chromosome via Meiosis
• As a result, Fertilisation involves the fusion of two haploid gametes (Egg from Mother, and Sperm from father), resulting in the formation of diploid Zygote that will develop into an Embryo

MEIOSIS

Diagram showing the Process of Meiosis

MEIOSIS I Meiosis involves two stages of division, Meiosis I and Meiosis II In Meiosis I, DNA condenses to form Chromosomes (duplicated Sister Chromatids joined at Centromere) Each pair of Homologous Chromosomes then undergo Synapsis to form complex involving two pairs of Sister Chromatids These Sister Chromatids exchange Chromosomal material between them via Crossing over (recombination), resulting in genetically distinct Chromosomes Nuclear membrane breaks down to allow Chromosomes to randomly line up across the centre of cell Homologous Chromosomes are pulled to each end of the cell to form two Nucleus Nuclear membrane reforms and Cytoplasm divides to form two genetically distinct haploid daughter cells MEIOSIS II In Meiosis II, Nuclear membrane breaks down to allow Chromosomes to condense and randomly line up at the centre of cell As a result, Chromosomes are pulled to each end of the cell to form two Nucleus Nuclear membrane reforms and Cytoplasm divides to form two genetically distinct haploid daughter cells As each of the two haploid cells produced in Meiosis I undergoes this process, a total of four genetically distinct haploid daughter cells are produced as a result of Meiosis