<P> The relatively brief M phase consists of nuclear division (karyokinesis). It is a relatively short period of the cell cycle . M phase is complex and highly regulated . The sequence of events is divided into phases, corresponding to the completion of one set of activities and the start of the next . These phases are sequentially known as: </P> <Ul> <Li> prophase, </Li> <Li> metaphase, </Li> <Li> anaphase, </Li> <Li> telophase </Li> </Ul> <P> Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets in two nuclei . During the process of mitosis the pairs of chromosomes condense and attach to fibers that pull the sister chromatids to opposite sides of the cell . </P> <P> Mitosis occurs exclusively in eukaryotic cells, but occurs in different ways in different species . For example, animals undergo an "open" mitosis, where the nuclear envelope breaks down before the chromosomes separate, while fungi such as Aspergillus nidulans and Saccharomyces cerevisiae (yeast) undergo a "closed" mitosis, where chromosomes divide within an intact cell nucleus . Prokaryotic cells, which lack a nucleus, divide by a process called binary fission . </P>

When does chromosome replication occur in eukaryotic cell