|MadSci Network: Genetics|
Hi Lucinda - Sorry I am a little slow in responding to your question. Hope this is still in time to help you out. "Crossing over" is a fascinating phenomenon that takes place during germ cell formation. During meiosis, the paired chromosomes exchange corresponding pieces with each other. This causes a shuffling of genes between members of the chromosome pairs, so that genes inherited from the mother will end up on the same chromosome as genes inherited from the father once germ cell formation is complete. This has been used extensively to map genes in lower animals such as the fruit fly and leads to the concept of linkage analysis in humans and other higher animals. I'll refer you to a web site that gives a very nice explanation of the phenomenon and how it's used in mapping: http://library.thinkquest.org/18258/chromosome.htm Also, check out a book entitled "Time, Love, Memory: A Great Biologist and His Quest for the Origins of Behavior", by Jonathan Weiner. This has an excellent description of the phenomenon of crossing over as well as an historical account of its discovery by the great fly geneticist T.H. Morgan and his student Alfred Sturtevant.
Try the links in the MadSci Library for more information on Genetics.