Question

What is the purpose of Meiosis I and II?

Answer 1

Meiosis is a type of cell division which occurs in a diploid cell and gives rise to four haploid cells each having half the number of chromosomes as compared to the parent cell.
The division was first studied by Beneden (1887), Strasburger (1888), Sutton (1900), Winiwarter (1900) in different organisms. The term ‘meiosis’ was first introduced by Farmer and Moore (1905).

Complete Answer:
Meiosis involves two successive nuclear divisions, which occur one after the other. These two divisions are called –
Meiosis I – The chromosomes become genetically different due to crossing over and their number is reduced to half and also called heterotypic or reduction division. It is essential for sexual reproduction. It introduces variation by forming a new combination of genes and random assortment of paternal and maternal chromosomes. By abnormal disjunction it may cause chromosomal mutation.
Four phases in meiosis I are – prophase I, metaphase I, anaphase I and telophase I.
Meiosis II – The sister chromatids are separated and the chromosome number remains the same as produced after the end of the first division and also called homotypic or equational division. The main function of homotypic division or Meiosis II is to separate the chromatids of univalent chromosomes which become dissimilar due to crossing over. It takes place simultaneously in the two nuclei formed after meiosis I.
Four phases in meiosis II are – prophase I, metaphase I, anaphase I, telophase I.

Note:
The essential stages that take place during meiosis are –
Two successive divisions occurred between them without any DNA replication.
Formation of chiasmata and crossing over.
Segregation of homologous chromosomes.
Separation of sister chromatids.