Meiosis

• Cells in reproductive organs divide by meiosis to form gametes (sex cells)
• Meiosis is the process that reduces chromosome number from diploid to haploid
• 1. Each chromosome is duplicated and the nuclear membrane breaks down, forming x-shaped chromosomes. The maternal + paternal chromosomes pair up along the centre of the cell.
• 2. First division: the chromosome pairs line up along the centre of the cell and are then pulled apart with each moving to opposite sides of the cell so that each new cell only has one copy of each chromosome. The sections of DNA are swapped between maternal + paternal chromosome pairs, creating recombinant chromosomes.
• 3. Second division: the chromosomes line up along the centre of the cell again and the arms of the chromosomes are pulled apart.
• 4. A total of four haploid daughter cells are produced.
• Haploid cells contain half the number of chromosomes as a diploid cell (23)
• Diploid cells contain a full set of chromosomes (46)
• Importance: Meiosis produces gametes e.g. sperm & egg cells in animals and pollen grains & ovum cells in plants.
• Importance: Meiosis increases genetic variation of offspring.
• Importance: Meiosis produces variation by forming new combinations of maternal and paternal chromosomes every time a gamete is made, meaning that when gametes fuse randomly at fertilisation, each offspring will be different from any others.