Word: egg
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...first time, researchers have identified twins that are identical on their mother's side, but share only half of their father's DNA. The twins, now toddlers, have been described as "semi-identical" - caught somewhere between identical twins (the result of the cleaving of an egg fertilized by one sperm) and fraternal twins (the result of two eggs meeting two sperm). Lead investigator Dr. Vivienne Souter says that while the term semi-identical provides some idea of how the twinning occurred, it is "an oversimplification...
...According to a study published in the Mar. 28 issue of Human Genetics, two sperm fertilized one egg and created the twins. The phenomenon occurs in about 1% of the population, but most embryos created in this way - called triploids because they have three sets of chromosomes - do not live. Says Dr. Mary Jane Minkin, a clinical professor of obstetrics and gynecology at Yale University: "This confirms that two sperm can get into an egg." Normally the cell dies. But Minkin makes a valid point: "Never say never in medicine and biology...
...study, Souter and her colleagues suggest that there are two ways this could have happened, depending on when the actual twinning event took place. In the first scenario, the egg might have divided in two (without separating) and then each part fertilized by one sperm. Egg division before fertilization is very rare, says Minkin. The second, more likely possibility is that the egg fused with two sperm cells and created a triploid cell. Then, at the second-cell stage, each shed the chromosomes from each of the sperm - or did something to correct its chromosomal count, says Souter. "There...
...think that the egg probably carried an X and one sperm an X, and one sperm a Y. It's possible that it is far more complicated than that. But that's the simplified explanation," says Souter. The twins have different proportions of male cells (XY) and female cells (XX), and are chimeric, meaning they have tissue with a diverse genetic make-up. Twin A, identified as a hermaphrodite, has 5% XY and 95% XX after genetic testing of the skin. Comparatively, Twin B, the male...
Make sure you can afford it. Think twice before lending money you are counting on having down the road. A ruined relationship is bad; a ruined nest egg is a disaster. If you can afford to lose the money, consider making it a gift from the start...