Polyploidy: Instant Speciation

Polyploidy: Instant Speciation - Another important mechanism known to generate new species is polyploidy. Polyploidy is a condition of having multiple sets of chromosomes rather than the normal haploid or diploid number. The increase in the number of chromosomes can result from abnormal mitosis or meiosis in which the chromosomes do not separate properly.

For example, if a cell had the normal diploid chromosome number of six (2n = 6), and the cell went through mitosis but did not divide into two cells, it would then contain 12 chromosomes. It is also possible that a new polyploid species could result from crosses between two species followed by a doubling of the chromosome number. Because the number of chromosomes of the polyploid is different from that of the parent, successful reproduction with the parent species would be difficult. This is because meiosis would result in gametes that had different chromosome numbers from the original, parent organism. In one step, the polyploid could be isolated reproductively from its original species. A single polyploid plant does not constitute a new species. However, because most plants can reproduce asexually, they can create an entire population of organisms that have the same polyploid chromosome number. The members of this population would all have the same chromosome number and would probably be able to undergo normal meiosis and would be capable of sexual reproduction among themselves. In effect, a new species can be created within a couple of generations. Some groups of plants, such as the grasses, may have 50% of their species produced as a result of polyploidy.

Many economically important species are polyploids. Cotton, potatoes, sugarcane, wheat, and many garden flowers are examples. Although it is rare in animals, polyploidy is found in a few groups that typically use asexual reproduction in addition to sexual reproduction. Certain lizards have only female individuals and lay eggs that develop into additional females. Different species of these lizards appear to have developed by polyploidy.

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