giv me a proper detailedexplanation of meiosis with different stages with proper diagram

Meiosis

• Specialized kind of cell division that reduces the chromosome number by half (thus called reductional division) resulting in production of haploid daughter cells (gametes)

• Haploid gametes fuse in sexual reproduction to give rise to diploid cells.

• Meiosis I starts after DNA has been replicated in S phase. Meiosis I is followed by meiosis II at the end of which four haploid cells are formed.

Meiosis I

• Meiosis I is divided into 4 phases.

• Prophase I − longest phase and is further sub-divided into 5 phases

  • Leptotene − Condensation makes chromosomes become distinct and compact.

  • Zygotene − Homologous chromosomes start pairing together by a process called synapsis to form a complex structure called synaptonemal complex. Two synapsed homologous chromosomes form a complex called bivalent or tetrad.

  • Pachytene − Longest phase of prophase I
    Recombination nodules appear in this stage at the sites where crossing over has to take place between non-sister chromatids of homologous chromosomes.

     

    Actual reason for genetic difference in progenies Crossing is mainly responsible for the genetic difference. Crossing over is the exchange of genetic material between two homologous chromosomes with the help of enzyme recombinase. It results in recombinant homologous chromosomes.

  • Diplotene − Synaptonemal complex dissolves and recombinants separate from each other except at crossover sites to form X-shaped structure called chiasmata.

  • Diakinesis − Chiasmata terminalises and chromosomes condense. Meiotic spindle assembles and nucleolus and nuclear envelope disappear.

• Metaphase I − Bivalent chromosomes align on the equatorial plate and spindle fibres appear and attach to the homologous chromosomes.

• Anaphase I − Homologous chromosomes separate; sister chromatids remain attached at their centromeres.

• Telophase I − Nuclear membrane and nucleolus reappear. Cytokinesis follows.

• Interkinesis − Stage between meiosis I and meiosis II
   

Meiosis II − Resembles Mitosis

• Prophase II − Chromosomes become compact and nuclear membrane disappears.

• Metaphase II − Chromosomes align on equatorial plate and spindle fibres appear and attach to kinetochores of sister chromatids.

• Anaphase II − Centromere of each chromosome splits and sister chromatids move towards opposite poles of the cell.

• Telophase II − Nuclear envelope reappears and cytokinesis follows, resulting in formation of a tetrad (4 haploid cells).
  

Significance of Meiosis

• It results in reduction of chromosome number by half in gametes, which again doubles during fertilization. Therefore, it helps to conserve the chromosome number of species from generation to generation.

• Crossing-over, occurring in pachytene stage of meiosis I, is a source of genetic variability in sexually reproducing organisms.

• The variation thus formed serves as the raw material for evolution.