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MEIOSIS

MEIOSIS. Mrs. Esserwein 2014. MITOSIS (Let’s review!). MEIOSIS. Makes sex cells (eggs and sperm) Meiosis is a cell division process that reduces the number of chromosomes by half! Human egg cell (23 chromosomes) Human sperm cell (23 chromosomes)

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MEIOSIS

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  1. MEIOSIS Mrs. Esserwein 2014

  2. MITOSIS(Let’s review!)

  3. MEIOSIS • Makes sex cells (eggs and sperm) • Meiosis is a cell division process that reduces the number of chromosomes by half! • Human egg cell (23 chromosomes) • Human sperm cell (23 chromosomes) • New cell that forms when egg cell and sperm cell join has 46 chromosomes. • There are 2 main stages (divisions) of Meiosis

  4. MEIOSIS (continued) • 4 cells are created where there was originally one. • That’s 4 cells with half of the amount of DNA needed by a cell! • When a cell goes through meiosis, it’s not concerned about creating another working cell. • Happens when it’s time to reproduce an organism. • Two IPMAT’s in a row! • Interphase that happens between the two processes is very short. • DNA is not duplicated.

  5. MEIOSIS (CONTINUED) • Great process that shuffles the cell’s genes around. • Plants, animals and sometimes even fungi undergo meiosis • Instead of creating two new cells with equal numbers of chromosomes (like mitosis), the cell does a second division soon after the first. • 2nd division divides the number of chromosomes in half. • Half the number of chromosomes = haploid cell • Haploid means half the regular number. • Diploid is the opposite (two strands) • Normal cells are considered to be diploid cells.

  6. Step One • MEIOSIS I: • Like the PMATI of a regular mitosis. • Pairs of chromosomes are lined up at the center of the cell and then pulled to each side. • Meiosis is a bit different because there something called crossing-over happens with the DNA.

  7. Crossing over is an exchange of genes. • The genes are mixed up, not resulting in a perfect duplicate like mitosis. • The cell divides, leaving two new cells with a pair of chromosomes each.

  8. Step Two • MEIOSIS II: • In Prophase II the DNA that remains in the cell begins to condense and form short chromosomes. • Each chromosome pair has a centromere. • The centrioles also begin their journey to opposite sides of the cell.

  9. In Metaphase II: • All of the chromosomes line up along the center of the cell • The centrioles are in position for the duplication.

  10. Anaphase II • The chromosomes split and move to opposite sides of the cell. • Each one splits into two pieces. • They don't divide up the DNA between the new cells; they split the DNA that exists. • Each daughter cell will get one-half of the DNA needed to make a functioning cell.

  11. Telophase II • Shows the DNA completely pulled to the sides and the cell membrane begins to pinch. • When it's all over, you are left with four haploid cells that are called gametes. • The eventual purpose of the gametes will be to find other gametes with which they can combine. • When they do, they will form a new organism.

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