Comprehension:
Restriction Enzymes
Read the following passage carefully and answer the given questions.
Genetic engineering is the combination of techniques to alter the chemistry of genetic material (DNA and RNA), to introduce these into host organisms and thus change the phenotype of the host organism. The first restriction endonuclease–Hind II, whose functioning depended on a specific DNA nucleotide sequence was isolated and characterised five years later. It was found that Hind II always cut DNA molecules at a particular point by recognising a specific sequence of six base pairs. This specific base sequence is known as the recognition sequence for Hind II. Besides Hind II, today we know more than 900 restriction enzymes that have been isolated from over 230 strains of bacteria each of which recognise different recognition sequences. Restriction enzymes belong to a larger class of enzymes called nucleases namely exonucleases and endonucleases. The DNA fragments can be separated according to their size through sieving effect by gel electrophoresis. Hence, the smaller the fragment size, the farther it moves.
Why are the techniques of genetic engineering based on use of gene cloning and gene transfer ?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → To overcome the limitation and allows to isolate and introduce only desirable genes without introducing undesirable genes into target organism.
(1) To overcome the limitation and allows to isolate and introduce only desirable genes without introducing undesirable genes into target organism. — Correct. In traditional hybridisation, whole sets of genes are crossed, so the undesirable genes come along with the desired ones. Gene cloning (making many copies of a gene) and gene transfer overcome this. A breeder can isolate one gene or a few desirable genes and introduce only these into the target organism.
(2) To induce the variation and generate the mixed copies of any unknown genes — Incorrect. Genetic engineering works with a chosen, known gene. It does not make mixed copies of unknown genes.
(3) For the inclusion and multiplication of undesirable genes along with the desired genes — Incorrect. This is the problem of traditional hybridisation. Genetic engineering was developed to avoid it.
(4) To work in larger scale to remove the unwanted copies of desirable genes in target organism — Incorrect. The aim is not to remove copies of desirable genes. The aim is to introduce only the wanted gene.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Principles of Biotechnology – “… Traditional hybridisation procedures used in plant and animal breeding, very often lead to inclusion and multiplication of undesirable genes along with the desired genes. The techniques of genetic engineering which include creation of recombinant DNA, use of gene cloning and gene transfer, overcome this limitation and allows us to isolate and introduce only one or a set of desirable genes without introducing undesirable genes into the target organism.”