MITOSIS AND
MEIOSIS
Copyright © 2006, D. B. Fankhauser,
Professor of Biology and Chemistry
University of Cincinnati Clermont College,
Batavia OH 45103
Sprouting onion
roots
for preparation of
root tips
chromosomes
File "Mitosis_Meiosis.html" was last modified on 09
Dec 2008.
Meiosis telophase
II
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In the 1870s, Walther Flemming noted that during cell division, thread-like
features were distributed to each of the new daughter cells. He termed this process
“mitosis,” or the process of the threads. Waldeyer named these threads
“chromosomes” in 1888. We now know that the purpose of mitosis is to distribute
genetically identical copies of genetic material to each of the two daughter cells.
We can see the stages of mitosis in rapidly dividing tissues (high mitotic rate)
such as in the root tips of growing seeds or bulbs. Plant tissues capable of mitosis are
termed meristematic tissues, found as lateral meristem by which the stem widens and
apical meristem, by which the stems lengthen. We can see mitosis in action in root
tips of sprouting onion (Allium sp.) Because they are particularly large, and the
mitotic rate is high. We will use onion root tips as a classic example of mitosis in
general, and in plants in particular.
Mitosis in animals has certain important differences from that of plants, as will
be demonstrated by studying this process in Ascaris, a genus of nematode to which
the common intestinal round worm belongs.
Make five drawings for each species, one in interphase, and four for each of the
stages of mitosis: prophase, metaphase, anaphase and telophase. As you make your
drawings, pay particular attention to the differences as well as the similarities between
animals and plants.
Meiosis is an entirely different form of cell division used to reduce the number of
sets of chromosomes during gametogenesis. We will study meiosis in the monkey
testis.
MITOSIS IN PLANTS: ONION ROOT TIPS
The images of onion root tip mitotic figures were taken of specimens prepared in our
lab according to our protocol Chromosomes in Root Tips..
Stage of
mitosis
Prophase:
Metaphas
e:
Anaphase:
Images
Description
The nuclear
envelope
dissappears, the
chromosomes
condense, often
appearing as a
"ball of yarn."
(The second
image also
contains a late
anaphase cell on
the right of the
image)
Microtubules
assemble,
forming the
spindle. Centrom
ers attach the
chromosome to
the spindle which
manoeuvers the
chromosomes to
the center of the
cell. The spindle
is visible in these
images.
Centromeres
split, and the
kinetochore
component of the
centromere pulls
the chromosome
along the
microtubule
towards the end
of the cell. this is
by far the shortest
phase, and
anaphase figures
are therefore less
common in these
preparations.
Chromosomes
have reached the
ends of the cell
and appear tighly
contracted. The
spindle will
dissolve, nuclear
membrane
reform, and
cytokinesis will
divide the cell
into two
genetically
identical daughter
cells.
Telophase
:
MITOSIS IN ANIMALS: ASCARIS
Stage of Mitosis
Prophase
metaphase
anaphase
telophase
Photograph of the stage in Ascaris