EXPLANATION OF MEIOSIS

EXPLANATION OF MEIOSIS
This type of cell division takes place in gonads during gametogenesis only. It consists of two successive divisions called first meiotic and second meiotic divisions. It is during the interphase of first meiotic division that the DNA is replicated in the usual manner leading to tetraploid amount of DNA in diploid
Number of chromosomes and during first meiotic division only the amount of DNA is reduced to diploid amount in each chromosome and chromosome number is also halved to haploid. In meiosis II the DNA in each new daughter cell is reduced to haploid, the chromosome number remaining haploid.
Both the first and the second meiotic divisions can be further subdivided into the same four stages- prophase, metaphase, anaphase, telophase each with few differences in the behavior of chromosomes and duration of phase.
First Meiotic Division
· Interphase: The DNA content of chromosome is doubled i.e. it is tetraploid.
· Prophase: This phase is of longer duration and complex and differs distinctly from mitotic prophase. It can be divided into following 5 stages.
(a)Leptotene stage
(b)Zygotene stage
(c) Pachytene stage
(d)Diplotene stage
(e)Diakinesis stage
· Metaphase I: It is similar to the metaphase of mitosis, the difference being only that it is homologous pair of chromosomes which lie parallel on the equator of spindle of microtubules with one member on the either side of the equator.
· Anaphase I: it differs from anaphase of mitosis in that the centromere does not split. So that one whole chromosome of homologous pair moves apart to reach the opposite poles of cell. This results in haploid number of chromosomes in each daughter cell i.e. 23 chromosomes consisting of two chromatids.
· Telophase: As there is random positioning of maternal and paternal bivalent chromosomes there is random assortment of maternal and paternal chromosomes in each daughter cell produced by cytoplasmic division during telophase.