Question

To investigate the possible presence of introns in three newly discovered genes (X, Y, and Z), you perform an experiment in which the restriction enzyme HaeIII is used to cleave either the DNA of each gene or the cDNA made by copying its mRNA with reverse transcriptase. The resulting DNA fragments are separated by gel electrophoresis, and the presence of fragments in the gels is detected by hybridizing to a radioactive DNA probe made by copying the intact gene with DNA polymerase in the presence of radioactive substrates. The following results are obtained:
Source of DNA Number of Fragments After Source Electrophoresis
Gene X DNA 3
cDNA made from mRNA X 2
Gene Y DNA 4
cDNA made from mRNA Y 2
Gene Z DNA 2
cDNA made from mRNA Z 2

Required:
a. What can you conclude about the number of introns present in gene X?
b. What can you conclude about the number of introns present in gene Y?
c. What can you conclude about the number of introns present in gene Z?

Answer 1

Answer:

a). At least one intron must be present in gene X.

b). At least two intron must be present in gene Y

c). It is impossible to determine whether there are any introns in gene Z.

Explanation:

Introns may be defined as the segments in the RNA molecule or the DNA molecule that does not code for proteins and they interrupts the sequences of each of the molecules.

In the context, we get :

a). In the gene X, at least one of the intron is present. Sometimes more than one introns may also be present. Due to slicing, we get one band less in the cDNA which is made from the mRNA.

b). In dene Y, at least one intron is present. Sometimes more than one introns are present inside the gene Y. In this case we get two bands less in the gene due to slicing.

c). In gene Z, it is not possible to determine the number of introns present in them. In genes X and Y, the Haelll enzyme is present in the intron. Therefore we get less of band after splicing the mRNA to cDNA.