NCERT Class 12 Biology: Chapter –6 Molecular Basis of Inheritance Part 8

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Question 17:

Now, sequencing of total genomes getting is getting less expensive day by the day. Soon it may be affordable for a common man to get his genome sequenced. What in your opinion could be the advantage and disadvantage of this development?



1. It would lead to better diagnosis, treatment and prevention of genetic disorders.

2. Better understanding of DNA gene sequence would lead to better understanding of biological systems.

3. Health care, agricultural and environment can be understood easily by learning the DNA sequencing of other living organisms.

4. Extensive research on human evolution can be done

5. DNA forensics would also become possible.


1. Patenting of the genetic test results can be done. In turn of which gene patenting can also be done.

2. Untreatable genetic disorders might be discovered.

Question 18:

Would it be appropriate to use DNA probes such as VNTR in DNA finger printing of a bacteriophage?


1. VNTR is the Variable Number of Tandem repeats. It is a chromosomal region. In which a small stretch of DNA sequence is repeated numerous times in a single location.

2. These VNTR produce a pattern of bands which is unique for each individual. These VNTR are used to identify criminals in forensic departments.

3. DNA fingerprinting is not an option for bacteriophage as it does not have repetitive sequencing portions like in VNTR’S so a pattern of bands would not be formed. Bacteriophage has a small genome that has all the coding sequences.

Question 19:

During in vitro synthesis of DNA, a researcher used 2’, 3’ – di deoxy cytidine triphosphate as raw nucleotide in place of 2’-deoxy cytidine. What would be the consequence?


Polymerisation would not take place as the group on the sugar is not present to add a nucleotide for forming ester bonds.

Question 20:

What background information did Watson and Crick have made available for developing a model of DNA? What was their contribution?


Watson and Crick have made information available for developing a model of DNA which are as follow:

1. Chargaff’s rule: They used Chargaff’s rule of base pairing which showed Adenosine forms bond with Thymine (A&T) and Guanine bonds with Cytosine (G & C).

2. Wilkins and Franklin’s rule: This rule was used to know that DNA has a diameter of 20 Å, a regular helix structure with 34Å distance and 10 base pairs of nucleotides in each turn of the spiral.

3. X-ray crystallography is was used to study DNA’S physical structure.


1. They discovered DNA was a double helix structure.

2. They also discovered the complementary base pairing by hydrogen bonds.

Question 21:

What are the functions of (i) methylated guanasine cap, (ii) poly-A “tail” in a mature on RNA?


(i) Methylated guanasine cap: When translation is initiated methylated guanosine, cap helps to bind mRNA to smaller ribosomal subunit.

(ii) Poly-A “tail”: It prolong mRNA’s life.

Question 22:

Do you think that the alternate splicing of exons may enable a structural gene to code for several isoproteins from one and the same gene? If yes, how? If not, why so?


The alternate splicing of exons is very specific in nature it could be either gender specific, developmental stage specific etc. Which can lead to encoding of various proteins from a single-gene. In absence of such splicing there is a requirement of new gene for every protein or is protein.

Question 23:

Comment on the utility of variability in number of tandem repeats during DNA finger printing.


Tandems is a chromosomal region in which a small stretch of DNA sequence is repeated numerous times in a single location. It forms a pattern of bands which is unique for each individual and is used in DNA fingerprinting in forensic department