English: Vectorised version of
File:Three cell growth types.png.
Three types of
cell reproduction are compared: the relatively simple
Binary fission and two more complicated types that either involve
mitosis or
meiosis.
Binary fission. Organisms such as bacteria typically have a single
chromosome (green). At the start of the binary fission process, the
DNA molecule of the cell's chromosome is
replicated, producing two copies of the chromosome. A key aspect of bacterial cell reproduction is making sure that each daughter cell gets a copy of the chromosome.
Cytokinesis is the actual physical separation of the two new daughter cells.
Cell reproduction that involves mitosis. Most
eukaryotic organisms like
humans have more than one chromosome. In order to make sure that a copy of each chromosome gets
segregated into each daughter cell, the
spindle apparatus is used (blue threads). The chromosomes are moved along the long thin
microtubules like trains moving along train tracks. Humans are
diploid; we have two copies of each type of chromosome, one from the father (red) and one from the mother (green).
Cell reproduction that involves meiosis. The human sex cells (
gametes) are produced by meiosis. For
sperm production there are two cytokinesis steps that produce a total of four cells, each with half the normal number of chromosomes. The situation is different in the
ovaries for
egg production where one of the four sets of chromosomes that is segregated is placed in a large egg cell, ready to be combined with the DNA from a sperm cell (see
meiosis for details).
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