Re: How can genetic engineering result in species hybridisation?

Dear Lynsey,

Species hybridization is a process that occurs naturally, or can be induced artificially.

Historically, the first artificial species hybrid was created by G. Karpechenko in 1928. He crossed cabbage plants with radish plants. These two plants are closely related (phylogentically) and their nuclei have the same number of chromosomes (2n=18). The hybrid plants that resulted were sterile, since they contain 9 cabbage chromosomes and 9 radish chromosomes which don't pair correctly in meiosis.

However, sometimes a part of the hybrid offspring produced seeds. This part of the plant contained double the number of chromosomes, an accidental and spontaneous mutation. This doubling allows for proper chromosome pairing in meiosis. The plants derived from these seeds had characteristics of both cabbage and radishes, yet was a new species distinct from either.

In nature, this process has occurred naturally. The classic example is the evolutionary history of wheat, genus Triticum. The modern bread wheat, T. aestivum, is a hybrid and one of its predecessors is a hybrid as well.

In general, to create hybrid species artificially, the following are required:

• Two species that are closely related and have the same number of chromosomes. This process only occurs in plants, because they are more tolerant to changes in chromosome number.
• The two plants are crossed to create a hybrid plant.
• To increase the frequency of chromosome doubling, the hybrid plant is treated with a chemical agent, such as colchicine. This generates fertile seeds of the hybrid species.

Your MAD Scientist,
Raymond Cheong

References:

Griffiths, A.J.F., Gelbart, W.M., Miller, J.H., Lewontin, R.C. Modern Genetic Analysis. (New York, W.H. Freeman & Co., 1999.)