CELL DIVISION.pdf

the formation of daughter cells from The sister chromatids arrive at a single parent cell. The new cells opposite ends of the cell. A new necessary for growth and tissue nuclear membrane begins to form repair are formed through mitosis around each set of chromosomes. and the rep...

the formation of daughter cells from The sister chromatids arrive at a single parent cell. The new cells opposite ends of the cell. A new necessary for growth and tissue nuclear membrane begins to form repair are formed through mitosis around each set of chromosomes. and the reproductive cells are The chromosomes decondense, so formed through meiosis. they are no longer visible under a light microscope. The nucleolus During mitosis, a parent cell divides reappears, and the mitotic spindle to form two daughter cells with the disappears. same number and type of DNA as the parent cell. The first phase of mitosis is prophase. During prophase, the cell’s chromosomes condense and become visible under a light microscope. The nucleolus (the part of the nucleus where ribosomes are made) disappears, and the mitotic spindle (a cell structure made of microtubules) begins to form. The microtubules move the chromosomes until they are lined up along the middle of the cell. This line of chromosomes is called the metaphase plate. The chromosomes are pulled apart by the microtubules. Each chromosome is separated into two, genetically identical sister chromatids, which are pulled to opposite ends of the cell.  known as independent segregation. This is done to further Almost all of your body’s cells divide increase genetic diversity among by mitosis. Meiosis is used to daughter cells. produce only one type of cell, and those are the gametes. During meiosis, a diploid cell divides to The chromosomes arrive at opposite produce four, non-identical haploid ends of the cell, and the cytoplasm daughter cells, each containing a is split by cytokinesis. single set of chromosomes. In humans, these are sperm and egg The first round of cell division is cells. complete. The two non-identical, haploid daughter cells now enter the second stage of meiosis. In early prophase I, at the beginning of meiosis each of all 46 chromosomes consists of 2 the chromosomes each consists of 2 chromatids connected by a chromatids centriomere. the chromosomes condense and form homologous pairs. Each homologous pair of the chromosomes align along the chromosomes lines up carefully so center of the cell their genes are aligned. Next, the chromosomes swap genetic material with one another, in a process the chromatids separate at the known as crossing over. This centromere. ensures that each sister chromatid is no longer genetically identical. each daughter cell receives 1 of the chromatids from each chromosome. The homologous chromosome pairs When the centromere separates, line up along the metaphase plate in each of the chromatids is again the middle of the cell. called a chromosome. At the end of the telophase II, there are 4 daughter cells, each containing 23 The homologous pairs are separated chromosomes. by the microtubules and are pulled to opposite ends of the cell. The homologous pairs line up and are separated at random in a process