Fall 2000 Biology 104 Fall 2000 Lecture 27 Monday October 30 Mitosis 1. Life proceeds by division of cells. For single-celled organisms this also comprises reproduction. Bacteria have single circular DNA molecules of 1-5 million base pairs.
Eukaryotes typically have their DNA arranged in a number of linear chromosomes.
These range in number from one to hundreds. The Drosophila fruit fly has four , while we humans have 23 . The DNA is organized by the histones and other proteins into nucleosomes and hence chromatin . In somatic cells, after replication of each chromosome, the identical sister chromatids must be reliably segregated into the two daughter cells so each is identical to the parent with a full set. These structures come into play again by organizing microtubules that will attach to the centromeres of the chromosomes and separate the sister chromatids in a series of stages known as interphase , prophase , metaphase , anaphase , and telophase .