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  Section: Principles of Horticulture » Pollination and fertilization
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Cell Division

Pollination and fertilization
  Introductory principles
  The genetic code
  Cell Division
  Inheritance of characteristics
  Other breeding programmes
  The Plant Varieties and Seeds Act, 1964
  Gene Banking

When a plant grows, the cell numbers increase in the growing points of the stems and roots, the division of one cell producing two new ones. Genetic information in the nucleus is reproduced exactly in the new cells to maintain the plant’s characteristics. The process of mitosis achieves this. Each chromosome in the parent cell produces a duplicate of itself, thus producing sufficient material for the two new daughter cells. A delicate, spindle-shaped structure ensures the separation of chromosomes, one complete set into each of the new cells. A dividing cell wall forms across the old cell to complete the division.

In the anthers and ovaries (parts of the plant producing the sex cells; the pollen and ovules respectively) cell division needs to be radically different. Sexual reproduction involves the fusion of genetic material contributed by the sex cells of each parent (see fertilization). Half of the chromosomes in the cells of an offspring are therefore inherited from the male parent, and half from the female. To ensure that the chromosome number in the offspring is equal to that of the parents, the number of chromosomes in the male and female sex cells (pollen and ovule) must be halved. This halving is achieved by a special division process, meiosis, in the anthers and ovaries. It ensures the separation of each homologous chromosome from its partner so that each sex cell contains only one complete set of chromosomes. This cell condition is termed haploid.


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