STUDY HINTS

Genes are located on chromosomes, and the stable manner in which chromosomes are first replicated and then distributed to daughter cells during cell division is the basis for genetic inheritance. Since much of genetic theory is based on the behavior of chromosomes and the genes they carry, it is very important to understand clearly how nuclear division occurs. In this way you can predict its consequences and understand the effect of errors that might occur in it. Yet the subject of cell division is complex, with many new terms to memorize and numerous things happening simultaneously. It is a continuous process that has been divided into stages somewhat artificially, so that we can describe it conveniently. All of this makes it rather hard to grasp at the beginning. Do not despair! It is really much simpler than it looks at first. The secret is to learn in stages. First one must understand the “strategies” of mitosis and meiosis, and the differences between them.

Mitosis has evolved as a mechanism to distribute accurately a copy of each chromosome present in the original cell to two new cells. The “goal” of meiosis is quite different. Meiosis passes alternate (homologous) copies of each type of chromosome to daughter cells and reduces the total chromosome number by half. These different objectives require slightly different chromosome behaviors. We shall briefly summarize these two processes, keeping in mind the different strategies they represent.