Lab Notes and Procedures-10 Biology 1004

North Arkansas College

Topic: Mitosis, Meiosis & Chromosomes 

(Experiments 8 & 9)

1. Mitosis is an asexual process occurring in the somatic cells (body cells that are non-sexual).
2. Humans contain 46 chromosomes per cell or 23 pairs.
3. In these somatic cells, it is necessary to be able to distribute equal amounts of genetic information to offspring.

1. To make sure each cell obtains a full complement of inherited traits (chromosomes).
2. For survival and division.

4. Mitosis occurs in 4 phases.
5. During cell growth, the cells are in Interphase. The chromosomes are not visible. They appear as long threads of material called chromatin. This phase is characterized by protein/DNA synthesis.
6. Near the end of Interphase, the chromosomes shorten and thicken becoming visible as true chromosomes. Human somatic cells have 23 pairs of chromosomes.
7. 4 phases of true mitosis.

1. Nuclear membrane disappears.
2. Spindle fibers develop from centrioles that have moved to the opposite poles of the cell.
3. Chromosomes attach to the spindle fibers.

1. Chromosomes align themselves in the center of cell.
2. Centromeres duplicate, and each chromosome pair separates.

1. The cell becomes dramatically elongated (as poles move as far apart as possible). The spindle fibers become maximally elongated.
2. The chromosome pairs are pulled toward opposite poles of the cell.

1. Chromosomes arrive at opposite poles of cells.
2. Nuclear membrane begins to appear around the nucleus of each daughter cells genetic material. The 2 cells begin to be pinched off in the center (cleavage furrow develops).
3. The cells become completely pinched off and separate from each other by a process called cytokinesis in animal cells.

Mitosis allows one diploid cell (2N chromosomes) to produce 2 cells that are diploid.

Plants have no centrioles, no asters, and there is no cytokinesis during mitosis. The plant cell wall is rigid and forms a cell plate to separate dividing cells.

Look at slides of onion tip mitosis. Look for cells in different stages of mitosis. Most cells will be in Interphase.

Human Chromosome Analysis

1. The study of chromosomes is called cytogenetics.
2. Prior to 1956, it was only thought that cells contained between 37-46 chromosomes. With the advent of chromosomal staining techniques in 1956, it was determined that there are 46 chromosomes or 23 pairs.
3. These chromosomes can be divided into groups A-G on the basis of their size, appearance, shape, etc.
4. Chromosomes in Metaphase are the most condensed forms. They are attached to spindle fibers and are more easily stained.
5. We usually use 1 of 2 methods of staining:

1. Giemsa Stain - Chromosomes are smaller in appearance, and the banding is not as evident.
2. G-band Stain - Bands in chromosomes are readily visible. These bands are rich in guanine and cytosine content.

6. The Centromeres may occupy different locations in the Metaphase chromosomes.

1. If the centromere is in the center, it is metacentric.
2. If it is between the center and the end of the chromosome, it is called sub-metacentric.
3. If the centromere is near the end of chromosome, it is called acrocentric.

7. There is one long arm and one short arm of a chromosome.

Take 2 slides. Dip one in the dark purple Giemsa Stain. Dip the other slide in the light orange-red G-band Stain. Let slides dry. Then diagram them, and determine which chromosome number is associated with it. Look for the longest chromosome.

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