- Cell division.

 

Cell division

Two types of cell division: Mitosis and Meiosis

ü  Mitosis: occurs in somatic cells and results in cell duplication→ two diploid daughter cells which are genetically identical both to each other and the original parent cell.

 

ü  Meiosis: occurs in the germ cells of the gonads and is also known as ‘reduction division’ because it results in four haploid daughter cells, each containing just one member (homologue) of each chromosome pair, all genetically different.

Meiosis involves two divisions (meiosis I and II). The reduction in chromosome number occurs during meiosis I and is preceded by exchange of chromosome segments between homologous chromosomes called crossing over.

In males the onset of meiosis and spermatogenesis is at puberty.

In females, replication of the chromosomes and crossing over begins during fetal life but the oocytes remain suspended before the first cell division until just before ovulation.

Reference :  Essential revision notes for mrcpch, 3^rd ed.