Polyploids

Content

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

Polyploids are plants with cells containing more than the diploid number of chromosomes; e.g. a triploid has three times the haploid number, a tetraploid four times and the polyploid series continues in many species up to octaploid (eight times haploid). An increase in size of cells, with a resultant increase in roots, fruit and flower size of many species of chrysanthemums, fuchsias, strawberries, turnips and grasses, is the result of polyploidy. There is a limit to the number of chromosomes that a species can contain within its nucleus. Polyploidy occurs when duplication of chromosomes (see mitosis) fails to result in mitotic cell division. The multiplication of a polyploid cell within a meristem may form a complete polyploid shoot that, after flowering and fertilization, may produce polyploid seed. Polyploidy can occur spontaneously, and has led to many variant types in wild plant populations. It can be artificially induced by the use of a mitosis inhibitor, colchicine.