Cambridge O Level Biology · Syllabus 5090 · Development of Organisms and Continuity of Life
Reduction Division
What is Reduction Division?
A nuclear division that halves the chromosome number, taking a diploid nucleus with two sets of chromosomes to haploid nuclei with one set each. Meiosis is a reduction division; mitosis is not, because mitosis maintains the chromosome number.
This definition is part of the Development of Organisms and Continuity of Life chapter in Cambridge O Level Biology.
Reduction Division in context
Life is continuous because cells divide, and the two kinds of nuclear division do opposite things to chromosome number. Mitosis maintains the chromosome number and produces genetically identical cells, which is how an organism grows, repairs damaged tissue, replaces dying cells and reproduces asexually. Meiosis is a reduction division: it halves the chromosome number from diploid to haploid and produces genetically different cells, which is how gametes are made. Fertilisation — the fusion of a male and a female nucleus — puts the two haploid sets back together and restores the diploid number. In humans that cycle reads 46 → 23 → 46 in every generation, which is exactly why chromosome number does not double each time a child is born.
Questions students ask about Reduction Division
What is the difference between mitosis and meiosis?
Mitosis is nuclear division giving rise to genetically identical cells in which the chromosome number is maintained; it produces two cells and is used for growth, repair of damaged tissues, replacement of dying cells and asexual reproduction. Meiosis is a reduction division in which the chromosome number is halved from diploid to haploid, resulting in genetically different cells; it produces four cells and is used to make gametes. In humans, mitosis runs 46 → 46 while meiosis runs 46 → 23.