Mitosis And Meiosis Of Eukaryotic Organisms

1101 Words5 Pages
The cell is the basic unit of all life. All living things-- tigers, trees, elephants, and men-- are made up of cells. A cell is alive-- as alive as you are. It breathes, takes in food, and gets rid of waste. It grows and reproduces, or creates one of its own kind. (Garrod 36) Most cells reproduce by dividing, so that there are two cells where there once was one. (Akkas 78) Every living thing is made up of one or more cells, and each of these cells was produced by an already existing cell. New cells are formed by dividing, so that there are two cells were there once was one. One-celled plants and animals begin and complete their lives as single cells. (Kemp 12) Human beings and multicellular plants and animals also develop from a single…show more content…
We have seen that every species of life has a certain number of chromosomes in its somatic cells. These chromosomes exist in pairs. (Baserga Biology 98) The members of each pair are similar in size, shape, and hereditary contact. Man has a 23 pairs of chromosomes; frogs 13 pairs; and pea plants, 7 pairs. Suppose the egg and sperm cells had the same number of chromosomes as all the other cells in an organism. (Mitchison 95) If they united, the somatic cells in the off-spring of such a union would have twice the number of chromosomes they should have. (Baserga Biology 34) For example, human beings have 46 chromosomes in their somatic cells. If the father 's sperm cells and the mother 's egg cells also contained 46 chromosomes, their child 's somatic cells would have 92 chromosomes. The next generation would have 184, and so on. Thus the sex cells must have half the chromosomes found in somatic cells. This is accomplished by meiosis. Meiosis consists of two separate divisions of sex cells. In the first division, the chromosome pairs line up side by side. (Cameron 115) Each chromosomes duplicates itself. Each doubled pair then moves to the equator. Next, the members of each original pair and their duplicates move to the opposite poles. (Cameron 115) The cell divides. Each of the two daughter cells receives one member of each original pair of chromosomes and its duplicate. These two new cells divides immediately. This time the chromosomes do not duplicate themselves.
Open Document