MadSci Network: Molecular Biology |
Synapsis occurs during prophase I of meiosis. First, there is a loose pairing of homologous chromosomes followed by corssing-over or recombination. Homologous chromosomes are able to pair to each other because their sequences are essentially similar or even identical in some places. After this has occurred (or at least begun), then synapsis occurs. Synapsis is an intimate association between the homologous chromosomes. This intimate association is probably catalyzed by the formation of protein structures found between the synapsed chromosomes. These protein structures include two lateral plates connected to a central plates by filamentous layers. On either side of these protein plates is the DNA from the non-sister chromatids. What actually initiates this process is currently unknown. Also, the above description may not agree exactly with what your textbook states unless it is a very recent edition. Sorry that I couldn't answer your question more thoroughly, but this is an active area of research and hopefully someone will find the answer to your question shortly.
Try the links in the MadSci Library for more information on Molecular Biology.