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Biology LibreTexts

Unit 7: Cell Division

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    • 7.1: Chromosomes
      In eukaryotes, chromosomes consist of a single molecule of DNA associated with many copies of 5 kinds of histones. Histones are proteins rich in lysine and arginine residues and thus positively-charged. For this reason they bind tightly to the negatively-charged phosphates in DNA. Cchromosomes have a small number of copies of many different kinds of non-histone proteins. Most of these are transcription factors that regulate which parts of the DNA will be transcribed into RNA.
    • 7.2: The Cell Cycle
      A eukaryotic cell cannot divide into two, the two into four, etc. unless two processes alternate: doubling of its genome (DNA) in S phase (synthesis phase) of the cell cycle; halving of that genome during mitosis (M phase).
    • 7.3: Mitosis
      When a eukaryotic cell divides into two, each daughter or progeny cell must receive a complete set of genes (for diploid cells, this means 2 complete genomes, (2n) a pair of centrioles (in animal cells) some mitochondria and, in plant cells, chloroplasts as well some ribosomes, a portion of the endoplasmic reticulum, and perhaps other organelles,
    • 7.4: Polyploidy
      Cells (and their owners) are polyploid if they contain more than two haploid (n) sets of chromosomes; that is, their chromosome number is some multiple of n greater than the 2n content of diploid cells. For example, triploid (3n) and tetraploid cell (4n) cells are polyploid.
    • 7.5: Endoreplication
      Endoreplication is the replication of DNA during the S phase of the cell cycle without the subsequent completion of mitosis and/or cytokinesis. Endoreplication is also known as endoreduplication. Endoreplication occurs in certain types of cells in both animals and plants.
    • 7.6: Sex Chromosomes
      The nuclei of human cells contain 22 autosomes and 2 sex chromosomes. In females, the sex chromosomes are the 2 X chromosomes. Males have one X chromosome and one Y chromosome. The presence of the Y chromosome is decisive for unleashing the developmental program that leads to a baby boy.
    • 7.7: Meiosis
      Mitosis produces two cells with the same number of chromosomes as the parent cell. Mitosis of a diploid cell (2n) produces two diploid daughter cells. If two diploid cells went on to participate in sexual reproduction, their fusion would produce a tetraploid (4n) zygote. The solution for this problem is Meiosis.

    Thumbnail: Life cycle of the cell. Image used with permission (CC BY-SA 4.0; BruceBlaus).