Lab #
Karyotypes
Date
I. Purpose: How can chromosomes be observed for abnormalities? List the four steps.
CA Standard: (3-a) Students know how to predict the probable outcome of phenotypes in a genetic cross
from the genotypes of the parents and mode of inheritance.
Background: Having additional, missing or damaged chromosomes causes several human genetic
disorders. One way of studying human genetic disorders is to observe the chromosomes themselves. In order
to do this the cells from a person are grown in a laboratory (step 1). After the cells have reproduced a few
times, they are treated with a chemical that stops cell division at the metaphase stage (step 2). The cells are
treated further, stained, and then placed on glass slides (step 3). The chromosomes are observed under the
microscope where they are counted and checked for abnormalities and photographed (step 4). The
photograph is then enlarged and the chromosomes are individually cutout. The chromosomes are identified
and arranged in homologous pairs (matching chromosomes). This arrangement of homologous pairs is
called a karyotype. In this activity, you will use a sketch of chromosomes to make a karyotype and examine it
to determine the presence of any defects.
II. Materials:
chromosomes sheet
scissors
glue
textbook
III. Procedure:
1. Observe the karyotype in figure 1. Notice the two sex chromosomes are pair number 23 and do not look
alike. They are different because this karyotype is of a male. Males have an X and a Y sex chromosome.
Figure 1 shows a complete set of chromosomes with no genetic defects.
2. Study the human karyotype in Figure 2 (handout). Notice that 23 of the chromosomes are numbered 1-23.
3. To match the homologous chromosomes look carefully at the unnumbered chromosomes. Note their
overall size and the pattern of the light and dark bands. Write 1 next to the unnumbered chromosome that is
closest in appearance to chromosome 1.
4. Repeat step 3 for chromosomes 2-23. Note: Many genetic disorders involve missing or extra
chromosomes.
5. After you have identified all the unnumbered chromosomes, use scissors to cut them out. Arrange the
chromosomes in their appropriate place in the Calculation/Results section. Use Figure 1 as an example.
Figure 1
IV. Data/Observations
V. Calculations/Results
Glue your karyotype table here. Use Figure 1 as an example.
VI. Questions (Re-state the questions and answer in a complete sentence.)
1. How many chromosomes are present in your karyotype (the unknown)?
2. Is your karyotype that of a normal person or a person with a genetic disorder? What is the disorder?
3. How does the karyotype in Figure 3 differ from that in Figure 1? What disorder is shown in Figure 3?
4. How does the karyotype in Figure 4 differ from that in Figure 1? What disorder is shown in Figure 4?
5. What happens during meiosis that can result in the addition or deletion of a chromosome?
VII. Conclusion: (Re-state the purpose and answer it in a complete sentence.)