|MadSci Network: General Biology|
Dear Michael, I must admit I'm a little confused by your question, I hope we're talking theoretically here! But let me give you a brief description of how assisted reproduction is achieved. In vitro fertilisation (IVF) is the process of bringing a sperm and egg together outside of the body. Sperm is taken from the male and eggs are 'harvested' from the female usually after they have ovulated. The eggs are taken from the woman's reproductive tract. As women only ovulate one egg at a time, they are often given medication which causes them to ovulate several eggs to increase the chances of one of them being fertilised. Fertilisation of the egg takes place in a petri dish in a solution designed specifically for survival of both the eggs and sperm, this solution contains salts, proteins and amino acids, and is specific for the particular species because even at this early stage, different species of egg and sperm have different requirements. The petri dish is incubated for a set period (12 - 48 hours, again depending on the species) in an incubator set to body temerature and with a particular mixture of gases (oxygen, carbon dioxide and nitrogen). After this time the egg is washed and transferred to a new solution which will provide for its new requirements. Successful fertilisation is assessed by viewing the egg over the next few days, looking for cell divisions. The fertilised egg, or embryo, is then put back into the reproductive tract of the female and basically you just hope that it attaches itself to the uterus wall. Attachment of the embryo to the uterus is called implantation. An interface between the mother and embryo is set up which allows transfer of all the nutrients which the embryo needs. As you can imagine, this is a very intimate attachment, embryonic cells grow right into the mother's tissue to make the placenta and blood supplies are connected. If the embryo doesn't produce the right signals, or if the mother doesn't produce the right signals, the embryo will not be able to implant and in these cases the mother may see the embryo as 'foreign', and reject it, like an organ transplant is often rejected. Artificial insemination is the process where sperm is taken from the male and put into the female. So fertilisation occurs in her reproductive tract instead of in a petri dish. Now, concerning your question about cross species gestation, I'm afraid I don't know of any examples where this has been done and as far as I know, it's not possible. I am proud to call myself a mad scientist, but not that mad!!! What you may have heard about is a few cases where people have put an embryo into the reproductive tract of another species for a few days and it has been able to survive, but implantation has never properly occurred. If someone is reading this who has heard of cases where cross species gestation has occurred I would be interested to hear about it. Michael, I hope this information has been helpful and has answered your question.
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