Dizygotic twins develop as two separate embryos produced by two separate ova fertilised by two separate sperm. Also known as fraternal twins. See also: Monozygotic. DNA

Di-ribo-nucleic acid. The protein which encodes genetic information, and controls all things inherited. In plants and animals, the DNA is located in the chromosomes. Dodder

See: Cuscuta spp. Dolichos lablab

See: Lablab niger. Domestication

The process by which ancient cultivators changed wild plants into crop plants by artificial selection. Usually, domestication was a very gradual process in which cultivators tended to use their best plants as parents for the next crop, producing quantitative improvements. Occasionally, however, domestication would progress in sudden and dramatic developments, with qualitative changes, as when both the non-shattering and free-threshing forms of wheat were discovered.

These changes occurred thousands of years ago, and the descendants of those forms have been in continuous cultivation ever since. Ancient domesticators often achieved results that modern plant breeding cannot improve as, for example, with pineapples, bananas, olives, and the classic wine grapes.

A few plant species were domesticated quite recently. These include rubber (Hevea brasiliensis) and oil palm (Elaeis guineensis).

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