Understanding Karyotypes
Integrated Science 2 Name: Per:
Background
Several genetic disorders in humans are caused by additional, missing, or damaged chromosomes. One means of studying genetic disorders is to observe the chromosomes themselves. In order to do this, cells from an individual are cultured, or grown, in a laboratory. After the cells have reproduced several times, they are the best length for identification.
The cells are further treated, stained, and “harvested” on glass slides. Lab technicians observe the chromosomes under the microscope, counting the number of chromosomes and checking for abnormalities in several cells. Then a photograph is enlarged and the chromosomes are individually cut out. The chromosomes are identified and arranged in homologous pairs. Homologous chromosomes are the two matching chromosomes found in each cell of the body. The arrangement of homologous pairs is called a karyotype. After months of practice, lab technicians quickly and easily arrange the chromosomes in the karyotype.
In this investigation you will use a sketch of chromosomes to make a karyotype. This sketch represents the photograph that would be taken through the microscope. Making a karyotype will familiarize you with a standard laboratory technique.
Procedure
Part A.
1. Observe the karyotype in Figure 1. Notice that the two sex chromosomes, pair number 23, do not look alike. They are different because this karyotype is of a male, and a male has an X and a Y chromosome. A female has two X chromosomes.
Part B.
1. Study the image in Figure 2. This is what a geneticist would see before they pair up the chromosomes into a neat karyotype.
2. Figure 3 shows what the true karyotype of the chromosomes from Figure 2 would look like once finished.
3. Observe the karyotypes in Figure 4 and 5. Note the presence of any abnormal chromosomes.
4. Answer analysis questions 1-10.
Analysis Questions
1. How many autosomes are present in the karyotype represented in Figure 3?
2. How many sex chromosomes are present in the karyotype represented in Figure 3?
3. Are there any abnormalities in the karyotype represented in Figure 3? If so, where?
4. Is the karyotype represented in Figure 3 that of an unaffected person or a person with a genetic disorder? If it is the latter, identify the disorder.
5. Is the individual represented by the karotype in Figure 3 that of a male or a female? Explain how you determined this.
6. How does the karyotype in Figure 4 differ from the karyotpe in Figure 1? Does the karyotype in Figure 4 exhibit any genetic disorder? If so, identify the disorder.
7. How does the karyotype in Figure 5 differ from the karyotype in Figure 1? Does the karyotype in Figure 5 exhibit any genetic disorder? If so, explain how.
8. What happens during meiosis that ultimately results in a defect characterized by the addition of chromosomes? By the deletion of chromosomes?
9. Explain why an individual cannot survive without an X chromosome, but can survive without a Y chromosome.
10. The human male determines the sex of his offspring. Explain this statement.