How Can Karyotype Analysis Explain Genetic Disorders?

How Can Karyotype Analysis Explain Genetic Disorders?

Introduction:
A karyotype is a picture of an organism's genetic make-up in which the chromosomes of a cell have been stained so that the banding pattern of the chromosomes appear. Cells in Metaphase are stained to show distinct parts of the chromosomes. The cells are then photographed through a microscope and enlarged. The chromosomes are cut from the photograph and arranged according to size, shape, centromere position, and banding patterns. Karyotypes have become of increasing importance to genetic counselors as disorders and diseases have been traced to specific visible abnormalities of the chromosome.

Objectives:
1. Construct a karyotype form the metaphase chromosomes of a fictitious organism
2. Analyze prepared karyotypes for chromosome abnormalities
3. Identify the genetic disorders of six fictitious cows by using the cows' karyotypes
4. Hypothesize how karyotypes analysis can be used to explain the presence of a genetic disorder

Materials:
print-outs of the metaphase chromosomes from six cows (2 pages)
scissors
glue

For this lab, assume a new species of cow has been discovered. This cow has three pairs of very large chromosomes. Researchers have been able to trace 4 genetic disorders to specific chromosomal abnormalities found in this new species. Study the karyotypes of the the normal male and female cows as illustrated below. Note the normal male cow has a pair of sex chromosomes similar to those of the human male, one large and one small (Xy). The female has a pair of sex chromosomes similar to those of the human female, both large (XX). The sex chromosomes make up the third pair of chromosomes.

1. Read the descriptions of the genetic disorders, the chromosomal mutation that cause the disorder, and examine the pictures of the mutated cattle.

2. Obtain copies of the metaphase chromosomes for each of the 6 cows (print this sheet out).

3. Write a hypothesis to describe how karyotype analysis can be used to explain the presence of a genetic disorder. Use the Data and Observation Sheet and write you hypothesis in the space provided.

4. Cut out the “metaphase” cells for each of the six cows.

5. Obtain the “metaphase’ cell for cow 1 and cut out the chromosomes. Place them along the line for Cow 1 on the Data and Observations Sheet.

·  Arrange similar chromosomes (homologous pairs) as shown in the normal karyotype. Match up similar chromosomes by comparing their size, length of the arms, centromere position, and banding pattern. Be sure to line up chromosomes that resemble the first pair of the normal karyotype above the number 1, those that resemble the second pair above the number 2, and those that resemble the third pair (sex chromosomes) above the number 3.

·  Once the chromosomes are positioned, paste their centromeres to the straight line using the glue. This represents the karyotypes for one cow.

6. Repeats step 5 each cow.

7. Compare your karyotypes with the karyotypes of the normal cows and with the descriptions of the genetic disorders.

8. Complete Data Analysis: Table 2

9. Complete the Analysis Questions and Conclusion for this lab.

10. Turn in your Lab Sheet.

Metaphase Chromosomes of Cow 1 /
Metaphase Chromosomes of Cow 2

Metaphase Chromosomes of Cow 3 /
Metaphase Chromosomes of Cow 4

Metaphase Chromosomes of Cow 5 /
Metaphase Chromosomes of Cow 6
This disorder, known as 3 Eyes/2 Legs Disorder, appears when there is a monosomy of the sex chromosome pair. A single large chromosome produces a female cow with an extra eye and only 2 legs. A single small chromosome produces a male cow with the same condition. /
3 Eyes/2 Legs Disorder
Monosomy of Chromosome 3
Colored Spots Disorder appears to result from trisomy of the chromosomes of the second pair. The extra chromosome of the second pair produces sterile cows that have rainbow colored spots. Since sterility always results, the Colored Spots Disorder is not passed on to its offspring. /
Colored Spots Disorder
Trisomy of Chromosome 2
A duplication of a portion of a chromosome from pair 1 produces a cow with an extra leg and a gold coat with no spots. This disorder also causes green horns and produces blue banding on the nose. /
Duplication Disorder
Duplication of a portion of Chromosome 1
The deletion of a short segment of the large sex chromosome results in the loss of the tail and the utter. It also cause red dots on the coat and green hooves. /
Dotted Deletion Disorder
Deletion of segment of large Chromosome in pair 3