Mitotic Figures

In the laboratory exercise you are about to conduct you must be able to recognize cells in various stages of the cell cycle. For convenience, these stages will be listed here as interphase, prophase, metaphase, anaphase, and telophase. More information about the laboratory exercise is given in the laboratory manual. Given below are illustrations of some of the features you will be asked to find.

 

ROOT TIP First, you must be able to recognize where the mitotic figures are found. You will be looking for the figures in a series of prepared slides of onion (Allium) root tips. These root tips have been preserved, sectioned (cut into thin slices), and stained to make the nucleus and chromosomes more visible. Below is shown a typical section of an onion root tip.   Notice the lighter cells near the bottom. This is the root cap and contains few mitotic figures. Above the root cap, rising in columns, are groups of cells containing distinct mitotic figures. This is where you want to search for the figures you are to count. You must realize that cell cycle stages blend into one another, so it is often difficult to distinguish where one stage ends and another begins. What you need to look for are distinguishing characteristics of the stages. Some of these are given below.

 

INTERPHASE Below are illustrated a series of cells in interphase. Notice in figures I1 and I2 the complete nuclei with a rather smooth appearance. Figure I3 shows a closer view which includes the nucleolus. (Remember, the nucleolus does not disappear until prophase.)

I1	I2	I3

 

PROPHASE Shown below are a series of cells in prophase. Notice that the nuclei have a slightly more granular appearance than what you see in interphase. (In figure P1 some interphase cells are shown on the left and some prophase cells are shown on the right.) This is because the chromatin is beginning to condense into chromosomes. What you see as granularity is the chromosomes of the onion cells.

P1	P2	P3	P4	P5

 

METAPHASE At the metaphase stage the chromosomes are moved to near the center of the cell. This is illustrated in the photomicrographs below. Notice that in all of these cells the chromosomes are clumped together near the "equator" of the cell.

M1	M2	M3

 

 

ANAPHASE In anaphase the chromatids separate from each other and the chromosomes are moved to opposite poles of the cell. This is illustrated below. The chromosomes have been pulled apart by the mitotic spindle (parts of which can be seen between the chromosomes in figures A2, A3, A4, and A6). Figure A2 is an early anaphase while figure A6 is a late prophase, nearing telophase.

A1	A2	A3	A4

A5	A6

 

 

TELOPHASE Telophase in plant cells involves the reformation of the nucleus around the separated chromosomes and, in cytokinesis, the separation of the parent cell into two daughter cells. The latter takes place by the formation of a cell plate near the center of the parent cell. Some telophase illustrations are shown below.   Figure T1 shows a cell in early telophase where the cell plate is just beginning to form between the two sets of chromosomes. Figure T2 shows two interphase cells (at the top and bottom) surrounding a telophase cell. Notice that the telophase cell, although it looks like it is divided, is about the same size as the interphase cells above and below it and consists of two narrower cellular parts. (One of the ways of distinguishing a telophase cell from a prophase or interphase cell is that it tends to be narrower than the other two.) Figures T3, T4, and T5 show late telophase cells. (Remember, telophase undoes the processes of prophase.) Figures T3 and T4 are a bit earlier than T5; they exhibit granularities that are the chromosomes decondensing into chromatin. Figure T5 is very late telophase; the nucleus, and even the nucleolus, have reformed, but notice that the cells are still narrow and have not enlarged as they will in interphase.

 

T1	T2	T3	T4	T5

 

 

PRACTICE The key to doing well in this lab exercise is to practice identifying cells in the various stages of the cell cycle. A good place to do this is the following website at the University of Arizona: http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/cell_cycle.html This site simulates the observations you are to make in your lab experience. Other sites, listed below, may help in understanding the process of mitosis (and meiosis).

 

Additional Web Resources

http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/cell_cycle.html (lab simulation) http://www.life.umd.edu/CBMG/faculty/wolniak/wolniakmitosis.html (pictures)

Page obtained from link at URL: http://www.ric.edu/faculty/jmontvilo/109.htm Prepared by Jerome A. Montvilo, Ph.D. for the use of his students. Copyright © by Jerome A. Montvilo. All rights reserved. Please send questions, comments, or suggestions to jmontvilo@ric.edu. Last updated 9 January, 2008