|MadSci Network: General Biology|
No - an unborn child's DNA cannot be changed from intercourse with a different man. The unborn child's DNA is a combination of DNA from the egg (mother's) and the sperm (father's). Immediately upon fertilization (entry of of the sperm into the egg), there is a cascade of events that prevent any subsequent sperm from that same ejaculation from entering the egg (barriers to polyspermy). These are almost always successful - and when they fail, the fertilized egg is generally not viable and dies soon afterwards. Therefore, only one sperm from one man can possibly contribute to the unborn child's genetic make-up. Polyspermy In fact, by the time the newly pregnant woman has had intercourse with a different man, days later, the fertilized egg will have already undergone several cell divisions. Each cell of the developing embryo is a clone of the cells before it, containing DNA that is identical to the DNA from the original fertilization. Additional sperm added to the uterus will have no more effect on the developing embryo than adding sperm to the surface of a post-natal baby or a grown human. The sperm will not be able to get into the cells and cannot possibly have an effect on the DNA of the baby. Hope this helps! Sanjida Rangwala, PhD University of Pennsylvania
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