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More About Cellular Division

  • Cellular Division is vital to all life on earth. It is used in a number of ways throughout the natural world, and also by humans.

Clones

  • Clones are Genetically Identical Cells or Organisms that are derived from one parent. The offspring of an organism that reproduces Asexually (only one parent) are Clones.
  • Eykaryotic Cells that undergo Mitosis are Clones of the parent cell. It may be that the organism is single-celled, such as an Amoeba, in which case Mitosis is the means of Asexual reproduction.
  • Many plants can produce Clones, reproducing Asexually. For example, strawberry plant runners or plants of the genus Kalanchoe. This is known as Vegetative Propagation. Many plants that can reproduce in this way can also reproduce Sexually.
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  • Bacteria reproduce by Cloning, through a process known as Binary Fission, which is different from Mitosis. Mitosis refers to division involving Chromosomes, and Bacteria do not contain Chromosomes. Instead, they have a single, naked DNA strand in the Cytoplasm. They also have extra DNA in the form of Plasmids, which can be swapped with other bacteria.
  • Artificial Cloning is the process by which humans force the Asexual reproduction of organisms to produce Clones. Plants may be Artificially Cloned by growers to produce Genetically Identical Individuals. Since 1997, it has also been possible to Clone animals. This however raises many ethical issues.

Budding in Yeast

  • Yeast are single-celled fungal organisms that are Eukaryotes. They most commonly reproduce Asexually by Mitosis, but the process is slightly different from other forms of Mitosis, in that it involves Budding.
  • When the cell first begins to reproduce, a Bud is formed of the surface of the cell. The cell then proceeds through Interphase, duplicating its Chromosomes and Organelles.
  • Next the Yeast cell undergoes Mitosis, where the new Chromosomes and DNA are placed in the Bud. After this occurs, the Bud contains nucleus with an identical copy of the parent cell's DNA.
  • Finally, the Bud separates from the parent cell, producing a new Yeast Cell that is Genetically Identical to its parent Cell.
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Producing Genetically Different Cells

  • Many organisms reproduce Sexually, where half of the offspring's DNA comes from one individual, and half comes from another.
  • This involves the fusion of nuclei from two cells which contain half the Genetic Information of a normal cell. These cells are known as Haploid Cells. When they come together during Sexual reproduction, they produce a cell with a full set of Genetic Information, known as a Diploid Cell.
  • Almost all cells in a Eukaryotic organism are Diploid, containing a full set of Genetic Information. They contain a full set of pairs of Homologous Chromosomes (there are 23 pairs of Homologous Chromosomes in normal human cells).
  • Each Chromosome in a Homologous Pair contains the same Genes, but can contain different Alleles of these genes. One Chromosome comes from the father and one from the mother of the organism.
  • In order to produce Haploid Cells, which only contain one Chromosome of every Homologous Pair, a cellular division process called Meiosis occurs. Effectively, a parent cell divides into two daughter cells, giving one of its Chromosomes in every one of its Homologous Chromosome Pairs to each of its daughter cells.
  • The actual process is a little more complicated, and involves the formation of two intermediary daughter cells, and four Haploid cells. The result is effectively the same the same however.
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  • The Haploid Cells produced are Genetically Different from each other. These cells are referred to as Gametes, and are involved in Sexual reproduction.
  • One Gamete from each parent comes together to form a cell that contains half the Genetic Information of each parent. This cell is called a Zygote.