MEIOSIS

in voilk •  2 days ago

    MEIOSIS
    Meiosis is the process by which one diploid (2n) eukaryotic cell divides to generate four haploid (1n) daughter cells. Dipliod means the cells in which chromosomes are in pairs (homologous pair) while haploid means the cells with half the number of chromosomes i.e. chromosomes are not in the form of pairs.

    • The word meiosis comes from Greek word 'meioun' , meaning "to make smaller," since it results in a reduction in chromosome number.

    Phase of Meiosis

    Meiosis was discovered and described for the first time in 1876, by a German biologist Oscar Hertwig.The preparatory steps of meiosis are identical to the interphase of mitosis. Interphase is divided into the same threee phases i.e. G1, S phase, and G2. Interphase is following by meiosis I and meiosis II.
    MEIOSIS I
    In meiosis I, the homologous chromosomes in a diploid cells sseprate and so two haploid daughter cells are produced. It is the step in meiosis that generates genetic variations. Meiosis I occurs in two main steps i.e. Karyokinesis and cytokinesis. The karyokinesis of Meiosis I is subdivided into main prophase I, metaphase I, anaphase I, and telophase I.
    Prophase I
    Prophase I is the longest phase in meiosis. During this stage, chromatin condenses into chromosomes. The homologous chromosomes line up with other and form pairs by a process called Synapsis.Each pair of homologous chromosomes is callled bivalent. Each bivalent has four chromatids, so it may also be called a tetrad. The two non -sister chromatids of homologous chromosomes join each other at certain points along their length. These points of attachment are called chiasmata. In thge next stage, the non-sister chromatids of homologous chromosomes exchange their segments and the phenomeon is know as Crossing over
    CROSSING OVER

    Source of photo
    All data collected from my book of Science.

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