Meiosis: Reduction Division for Gamete Formation — NEET Biology

In contrast to mitosis, meiosis occurs in the diploid cells which are destined to form gametes. It is called the reduction division since it reduces the chromosome number by half while adding the gametes. In sexual reproduction when the two gametes fuse the chromosome number is restored to the value in the parent. Meiosis involves two successive nuclear and cell divisions (meiosis I and meiosis II) with a single cycle of DNA replication. Thus, four haploid gametes are formed from each diploid cell. Meiosis I is initiated after the DNA replication in the S phase. During anaphase I the bivalents arrange on the equatorial plate. This is followed by anaphase I in which the two chromosome of each bivalent separate and start moving towards the two opposite poles of the cell. The first meiotic division comes to an end with telophase I. The nuclear division in the first meiotic division is followed by the cytoplasmic division (cytokinesis). This is quite similar to mitosis. Each pole receives half the chromosome number of the parent cell. In telophase I, the nuclear membrane and nucleolus reappear. Meiosis II is similar to mitosis. During anaphase II the sister chromatids separate. Thus at the end of meiosis four haploid cells are formed.