Question

As a genetics graduate student, you have isolated a gene responsible for diabetes, but you find the corresponding mRNA is 450 bases shorter than the DNA sequence. Does this mean you have isolated the wrong DNA?

a. yes, mRNA and the DNA template should be the same length
b. no, mRNA has fewer bases because introns are removed
c. no, mRNA has fewer bases because exons are removed
d. yes, mRNA should contain more bases than the DNA sequence because exons are added

Answer 1

The mRNA is shorter than the DNA sequence because introns are removed during RNA splicing. This does not indicate that the wrong DNA was isolated, but rather reflects a normal step in gene expression. The correct answer is b. no, mRNA has fewer bases because introns are removed.

Step-by-step explanation:

The phenomenon you are describing where the mRNA is shorter than the DNA sequence is due to the process of RNA splicing. In eukaryotes, genes are composed of exons and introns. The exons are the coding sequences that ultimately get translated into protein. However, the introns are non-coding sequences that are present in the initial RNA transcript but are removed during RNA splicing. After the introns are spliced out, the remaining exons are joined together to form the mature mRNA molecule. This is why the mRNA is shorter than the DNA sequence.

Therefore, the correct answer to the question is: b. no, mRNA has fewer bases because introns are removed. This does not necessarily mean that you have isolated the wrong DNA; rather, it reflects a normal and crucial step in the expression of genes in eukaryotic cells.