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THE SAHARA

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Author Topic: THE SAHARA  (Read 4036 times)
Bianca
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« Reply #15 on: May 16, 2009, 11:05:20 pm »










“In human terms, this is the equivalent of a mother giving birth to a baby that is genetically unrelated to her, but genetically identical to the father,” explains Richard Primack, professor of biology at Boston University.

An experiment in which pollen from the Cupressus dupreziana was dusted onto the female cones of the Mediterranean cypress, whose resulting seeds were germinated and grown for 15 years, culminated in trees physically similar and identical in their DNA to the “father” tree, but unlike the “mother.” There is no obvious evolutionary advantage to this. If other conifer species were to grow nearby—and they do not—then perhaps the pollen of the Saharan cypress could be said to profit by “borrowing” these other cones, using their ovules merely as incubators. Even so, as in all cloning, this would lead to an evolutionary dead end: genetic invariability and a species not capable of adapting to changing conditions.

Rob Nicholson, head of the Smith College Botanic Garden in Northampton, Massachusetts, collected seeds in 1985 from cypresses in the Tassili to study artificial propagation methods. One tree he germinated in the greenhouse shot up so fast it had to be cut down in order to save the roof. He has sent hundreds of cuttings from seedlings to botanic gardens in Atlanta, Pasadena, Houston and elsewhere. “To see healthy trees growing in the ground that you have started years earlier from small cuttings is almost like seeing your own child graduate from college. You feel they’ve made it!” he says.

But these New World transplants are only the latest that, since the mid-20th century, have been grown outside their home habitat. France’s oldest botanical garden, the Jardin des Plantes in Montpellier, has eight healthy specimens of Saharan cypress, while the Villa Thuret in Antibes, France, which is part of the Institut National de Recherche Agronomique, has grown trees studied closely by Christian Pichot and Muhammad el Maataoui, who first discovered its unique genetic behavior.

It was long known that only about 10 percent of seeds from both wild and cultivated Saharan cypress trees have a viable embryo, so the tree’s low fertility rate was thought to be intrinsic to the species. Pichot and el Maataoui recently determined exactly why: The tree’s meiosis—its cell division prior to reproduction—is wildly erratic. Instead of the pollen dividing neatly in half to create a pair of diploid cells, which contain two sets of chromosomes, it often creates cells containing one or four sets of chromosomes —or none. Only diploid cells can successfully germinate.
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