Just a while ago, you had a brief review on the two types of cell division: Mitosis and meiosis. Do you know that these processes help maintain the number of chromosomes of organisms? Chromosomes are threadlike structure of DNA and protein that contains genetic information. There are two types of cells in the body- diploid and haploid. What is the difference between a diploid and haploid cell? A diploid cell contains two complete 5 sets of (2n) of chromosomes. Skin, blood, muscle cells (called somatic cells) and diploid. A haploid cell contains half the number as diploid cell (n) meaning they contain only one set of chromosomes. Humans for example are diploid; they have complete set of chromosomes. We inherited one set from the father and another set from the mother. Thus, humans have 2n = 46 chromosomes, where n = 23, or the haploid number of chromosomes. How does a cell maintain its number of chromosomes? Mitosis plays a significant role in this process. Mitosis is the process of cell division which produces diploid cells. Its purpose if for cell growth, repairs for damaged tissue and there are four stages of mitosis: prophase, metaphase, anaphase and telophase. Imagine mitosis as a graceful “dance” of choreographed chromosomes, centromere, spindle microtubules, nuclear membrane, and the nucleus. Chromosomes appear on stage, have partner, align in the middle and suddenly separate from each other with the active and lively participation of the other members of the dance. It takes place in the nucleus of the cell. The nucleus can be considered the stage. INTERPHASE Interphase takes place before the first stage of mitosis, the prophase. During interphase, the cell is not dividing at all; it merely grows. However, the DNA at this time is already duplicated. But you cannot see the individual chromosome yet because they are still loosely packed chromatin fiber – a combination of DNA and protein molecules. 1.PROPHASE The first appearance of the chromosome on stage to start the mitotic dance is during prophase. The chromosome can be clearly seen to consist of a pair of sister chromatids joined at the centromere. Chromatid is one of the two identical “sister” parts of a duplicated chromosome. The nucleolus disappears and the nuclear membrane starts to break down. The spindle microtubules start to form from the centrosomes moving towards the opposite poles. The chromatids are now attached to the spindle microtubules. They start pulling the chromosomes toward the center of the cell ready for the next step in the dance. 2.METAPHASE The next step of the mitotic dance is metaphase. Chromosomes are aligned at the middle of the cell. All the chromosomes are attached to the spindle microtubules which are now fully developed. The nuclear membrane has broken. The centrosomes are located at the opposite poles.
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