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Mitosis and Meiosis

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Introduction

Elmaz Korimbocus Mitosis and Meiosis MITOSIS a) Examples of where mitosis occurs in the body: - cell division is essential for growth, repair and reproduction, and replacing dead cells such as skin cells. b) The genetic information for a cell is stored in the nucleus, which contains coil-like structures known as chromosomes. They contain the genetic information encoded in DNA, which enables the cell to carry out its functions. c) If a cell needs to make two exact copies of itself, its nucleus needs to divide in order to pass its information to the two daughter cells. So there needs to be two sets of identical genetic information. d) A human cell has 23 pairs of chromosomes. e) Interphase: * Normal cell growth and metabolic function. * Synthesis of DNA. * Each chromosome homolog replicates, so that each homolog consists of two sister chromatids. * Normal growth and function. Prophase: * Chromosomes coil and condense. * 2 sister chromatids attached at centromere. * Homologs not associated with one another. * Nucleolus disappears, nuclear membrane breaks down. * Centrioles (organelle important in mitosis, see below) duplicates, spindle fibers extend from centrioles. Metaphase: * Nuclear membrane disappears, chromosomes maximally condensed. ...read more.

Middle

l) In mitosis, a single cell divides to form two daughter cells. These cells grow, and then divide to form a total of four cells. Those four cells grow and divide to form eight cells, etc. In meiosis, a single cell divides twice, resulting in four daughter cells that do not grow and divide again. Instead, these cells are modified to become eggs or sperm in humans. MEIOSIS 4. m) One of the most important requirements of a successful mitosis or meiosis is that the blueprint of life, the DNA, is provided in equal amounts to each of the daughter cells. The DNA in all human cells except eggs and sperm is housed in 46 chromosomes. Eggs and sperm consist of only half that number, 23 chromosomes per cell. Every person inherits one set of chromosomes from their mother (in the egg) and the other set of chromosomes from their father (in the sperm). It is imperative that when mitosis and meiosis are complete, the appropriate number of chromosomes exists in each cell. If there are extra or missing chromosomes, the cells usually do not live. To ensure that there are enough chromosomes to be divided evenly between the two daughter cells during mitosis, an essential step precedes cell division that allows the chromosomes to be copied, a step called DNA replication. ...read more.

Conclusion

Of the 23 pairs, 22 are essentially identical to each other. The 23rd pair is either a pair of X chromosomes, meaning the individual is female, or an X chromosome and a Y chromosome, meaning the individual is male. When humans produce sperm and eggs, the chromosome pairs separate and the egg or sperm receives only one member of each pair. Each sperm produced by a man has 22 chromosomes plus either an X chromosome or a Y chromosome. Each egg produced by a woman contains 22 chromosomes plus an X chromosome. Before the chromosomes separate in this way the pairs swap pieces of their DNA with each other. In women this process happens with all the chromosome pairs including the double X pair. However, because the X and the Y chromosomes in a man are so different they swap almost no DNA with each other when they separate. When the sperm and the egg join together in fertilization the individual chromosomes pair up again. New cells for growth and repair are made by mitosis which makes two identical new cells. These contain the same chromosome number. Asexual reproduction also involves mitosis. The other kind of cell division is called meiosis and it makes sex gametes. Each cell divides to make four new cells with half the number of chromosomes. ...read more.

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