Prophase is the first phase of mitosis, the process that separates the
duplicated genetic material carried in the nucleus of a parent cell into two
identical daughter cells. During prophase, the complex of DNA and proteins
contained in the nucleus, known as chromatin, condenses. The chromatin coils
and becomes increasingly compact, resulting in the formation of visible
chromosomes. Chromosomes are made of a single piece of DNA that is highly
organized. The replicated chromosomes have an X shape and are called sister
chromatids. The sister chromatids are pairs of identical copies of DNA joined
at a point called the centromere. Then, a structure called the mitotic spindle
begins to form. The mitotic spindle is made of long proteins called
microtubules that begin forming at opposite ends of the cell. The spindle will
be responsible for separating the sister chromatids into two cells. Prophase is
followed by the second phase of mitosis, known as prometaphase.