Cell and Molecular Biology Behrouz Mahmoudi Mitosis and Meiosis 1

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MITOSIS – “Double and Divide” 5

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MITOSIS: all duplicated chromosomes separate 7

Chromosomes in the prometaphase stage of mitosis, from a cell in the flower of Haemanthus. 8

MITOSIS steps 0-1 – Interphase and Prophase 9

MITOSIS steps 2-4– Metaphase, Anaphase, Telophase 10

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Centromere locations and designations of chromosomes based on centromere location. Note that the shape of the chromosome during anaphase is determined by the position of the centromere. 18

The phases of the cell cycle. Following mitosis (M), cells enter the G1 stage of interphase, initiating a new cycle. Cells may become nondividing (G0) or continue through G1, where they become committed to begin DNA synthesis (S) and complete the cycle (G2 and M). Following mitosis, two daughter cells are produced and the cycle begins anew for each cell. 19

The length of time spent in each phase of one complete cell cycle of a human cell in culture. Actual times vary according to cell types and conditions. 20

Mitosis in an animal cell with a diploid number of 2n = 4. The events occurring in each stage are described in the text. Of the two homologous pairs of chromosomes, one contains longer, metacentric arms and the other, shorter, submetacentric arms. The maternal chromosome and paternal chromosome of each pair are shown in different colors. Part (g) illustrates the formation of the cell plate and lack of centrioles in a plant cell. 21

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the formation of the cell plate and lack of centrioles in a plant cell. 27

The three major checkpoints within the cell cycle that regulate its progress. 28

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MEIOSIS MAKING REPRODUCTIVE CELLS (SPERM AND EGG) inr eproductive organs (testis, ovary) SIMILAR TO MEIOSIS BUT TWO STEPS, the idea is to reduce a double set to single – so single sets from two parents can join in fertilization to produce baby’s double set 30

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Homologous (matching) chromosomes come from your two parents – you have TWO SETS of chromosomes! 32

Overview of the major events and outcomes of mitosis and meiosis. Two pairs of homologous chromosomes are followed. 33

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The substages of meiotic prophase I 35

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The major events during meiosis in an animal with a diploid number of 2n = 4 beginning with metaphase I. Note that the combination of chromosomes in the cells produced following telophase II depends on the random alignment of each tetrad and dyad on the metaphase plate during metaphase I and metaphase II. Several other combinations (not shown) can also be formed. 37

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Spermatogenesis and oogenesis in animal cells. 39

Mitosis and Meiosis Compared 40

Alternation of generations between the diploid sporophyte (2n) and the haploid gametophyte (n) in a multicellular plant. This is an angiosperm, where the sporophyte stage is the predominant phase. 41

A diagram of the mitotic chromosome and its various components, showing how chromatin is condensed into it. 42