Biology 1001 Spring 2008 (B. Fall), Class notes, topic #6—Mitosis, meiosis
complete the reading assignment in your text (Freeman, Biological Science, 2
ed.): pp. 227-
237, 248-260, 263.
I also strongly recommend that you work through two tutorials on the Freeman companion website and CD
that are referenced below in the outline, part V.-A.: (Phases of mitosis; Meiosis). These are also on the
WebVista webpage for class 6.
1. Outline the basic sequence of events of mitosis.
2. Outline the basic sequence of events of meiosis.
3. Appreciate similarities and differences of mitosis and meiosis, including the outcome of each
4. Understand the meaning of homologous chromosomes and sister chromatids, the difference between
them, and their origins.
5. Relate the events of meiosis to the results of Mendel’s breeding experiments with peas.
: cell division
In prokaryotes (all unicellular), cell division (asexual reproduction) occurs by the process of
(not mitosis). Prokaryotic DNA is in the form of a single circular (i.e., joined)
In eukaryotes, there are two types of nuclear division:
two new nuclei with the same number of chromosomes as the original, with the same genetic
composition. Mitosis is important in growth of multicelled organisms, and replacement of
damaged or dead cells. In contrast, meiosis results in halving of the number of chromosomes in a
diploid cell, ultimately producing four haploid cells (gametes) with half the chromosome number
of the parent cell.
in eukaryotes refers to the life cycle of a cell, from its formation until it completes
division. The cell cycle consists of
(“between phases”) with
three stages (G
, S, G
the dividing phase
, with five stages. The stages are a continuum rather than
discrete. Mitosis itself comprises a relatively short part of the cell cycle; most time is spent in
stages (mnemonic: IPPMAT):
(replication of chromosomes (DNA synthesis) occurs during S stage); precedes
mitosis. DNA replication results in each chromosome having two genetically identical units,
. Thus in cells entering mitosis (as well as meiosis), each
chromosome has already been duplicated
(the first of five stages of mitosis proper)—chromosomes (each consisting of sister
chromatids) condense; centrosomes (in animal cells) move toward poles, and mitotic spindle