Chapter 23, Problem 1CONQ

A person with a rare genetic disease has a sample of her chromosomes subjected to in situ hybridization using a probe that is known to recognize band p11 on chromosome 7. Even though her chromosomes look cytologically normal, the probe does not bind to this person’s chromosomes. How would you explain these results? How would you use this information to positionally clone the gene that is related to this disease?  

Summary Introduction

To review:

Upon in situ hybridizations of the sample of the chromosome of an individual affected with a rare genetic disease, the probe that recognizes the p-11 band on chromosome 7 is unable to hybridize the affected chromosome. Also, determine the reason for the results and the ways through which positional cloning of the gene using the probe that is related to the disease.

Introduction:

The word insitu is derived from the Latin word that means in place. This suggests that the hybridization is carried out on the chromosome of interest that adheres to the surface by using a probe. This technique is basically employed to cryogenically map the gene locations of genes on the chromosome or DNA (deoxyribonucleic acid) sequences.

Explanation of Solution

The term insitu hybridization indicates the DNA sequence that forms the base pairs with a short complementary DNA strand called probe and forms a hybrid with the intact chromosome adhered to the surface. Labeled probes are used to detect the location of a gene present on the chromosome that is intact on the surface. The most common method of insitu hybridization is using fluorescently labeled probes called fluorescence insitu hybridization.

When a person suffersfroma rare genetic disease, it marks the deletion of the segment of a gene present on the chromosome kept intact on the surface. Due to the deletion of the segment of a gene on the chromosome, the probe fails to hybridize the DNA sequence due to lack of p-11 band present in the sequence of DNA on the chromosome. This situation marks the usage of molecular markers.

Molecular markers are the DNA sequence that do not encode for any gene along the chromosome. These molecular markers are the segments of DNA located at a specific site on the chromosome, which makes it easily recognizablethrough techniques like a polymerase chain reaction and gel electrophoresis.

The molecular markers help in cloning the segment of DNA that is lost in the affected individual but present in an unaffected individual. These molecular markers are known to be found near the p-11 band and their walking in any of the direction occurs. This experiment of using the molecular markers that walks in any of the direction to clone the lost segment of DNA in the affected individual is carried forth on an unaffected individual.

The comparison is made to the sequence of DNA obtained from the chromosome of an affected individual. This results in the yield of the clone of a segment of DNA sequence that is lost in the affected individual and found intact in an unaffected individual. This segment of DNA has a p-11 band that is recognized by the probe, and hence, the insitu hybridization takes place. The segment of a chromosome, which binds to the probe in an unaffected individual can now be cloned and multiplied using cloning techniques or genetic engineering.

Conclusion

Therefore, it can be concluded that the probe could not hybridize the DNA segment of an affected individual due to lack of p-11 band which is detectedby the probe. However, the cloning is carried forth using the molecular markers that tag the p-11 band on the unaffected DNA sequence that now hybridize to the probe.