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Hi Faezeh,
I think you are right (if I understand you right). Most cloning is done by removing the nucleus from an egg (1N) and replacing it with the nucleus from an adult cell that is diploid, a process called "nuclear transfer." The diploid nucleus comes from a "somatic cell," which means it's not a haploid germ cell such as a sperm or egg. Maybe your teacher meant that egg cell is not diploid? But the haploid (1N) egg has its nucleus removed anyway. For now, an egg is still absolutely necessary to grow a new embryo, whether it's a clone or not. When Dolly the sheep was cloned, they took the nucleus from adult cells in the mammary tissue of the adult sheep who was cloned to make Dolly. The adult cells were definitely diploid. Making embryos from haploid sperm and eggs (a test tube baby) isn't cloning. By the way, in 2007, researchers published that they were able to "reprogram" skin cells (diploid) to behave like human embryonic stem cells. These diploid cells can be cultured in a lab dish, and are therefore cell line clones (all genetically identical). But although these cells can differentiate into any kind of tissue and so could be useful for treating illnesses, like human embryonic stem cell lines, the reprogrammed skin cells don't develop into embryos, so it's not like cloning a sheep or a person. This new approach is good because it skips the need for human eggs AND it skips the human embryo stage. (However, it's not ready to used to cure anyone yet, because the cells might cause cancer. :( ) Most people know that lots of people don't think we should experiment with human embryos. But not everyone knows that embronic human stem cells are an ethical problem for another reason. In order to make human stem cells by nuclear transfer, you need hundreds of human eggs. To get them, you have to give lots of women heavy doses of hormones to promote the shedding of large numbers of eggs (instead of the usual one or two eggs), then a surgeon has to remove all the eggs from the women's ovaries. The hormones are probably bad for women's long-term health. To provide stem cells lines for each patient who had a disease like Parkinson's disease or Alzheimers, you would need to give heavy hormones to thousands and thousands of women "donors." Because women in places like the U.S. wouldn't want to risk their health without a good reason, the egg "donors" (who are actually usually paid for their eggs) would probably end of being poor young women in undeveloped countries and there is a good chance many would develop cancer or other health problems later in life from the heavy doses of hormones they got. So they would be sacrificing their health in order to help wealthier people in other countries. Many people think this is unethical. If scientists can safely make human stem cells from skin cells or other diploid cells instead of using eggs (which are haploid), that would be MUCH better! I know this isn't what you asked, but I couldn't resist talking about it. I hope I answered your question. :) Here's part of the article about skin cells turning into stem cells:
Researchers Turn Skin Cells Into Stem Cells
By Gretchen Vogel ScienceNOW Daily News 20 November 2007 Scientists have managed to reprogram human skin cells directly into cells that look and act like embryonic stem (ES) cells. The technique makes it possible to generate patient-specific stem cells to study or treat disease without using embryos or oocytes--and therefore could bypass the ethical debates that have plagued the field. "This is like an earthquake for both the science and politics of stem cell research," says Jesse Reynolds, policy analyst for the Center for Genetics and Society in Oakland, California. The work builds on a study published last year by Shinya Yamanaka of Kyoto University in Japan, which showed that mouse tail cells could be transformed into ES-like cells by inserting four genes (ScienceNOW, 3 July 2006). Those genes are normally switched off after embryonic cells differentiate into the various cell types. In June this year, Yamanaka and another group reported that the cells were truly pluripotent, meaning that they had the potential to grow into any tissue in the body (ScienceNOW, 6 June). Now the race to repeat the feat in human cells has ended in a tie: Two groups report today that they have reprogrammed human skin cells into so-called induced pluripotent cells (iPSs). In a paper published online in Cell, Yamanaka and his colleagues show that their mouse technique works with human cells as well. And in a paper published online in Science, James Thomson of the University of Wisconsin, Madison, and his colleagues report success in reprogramming human cells, again by inserting just four genes, two of which are different from those Yamanaka uses.. . |
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