Molecular Basis of Inheritance Test - 83

Molecular probe will be RNA or DNA molecule which are complementary to a part of desired gene. They will be radio isotopic in nature for easy tracking of the strands.

Feulgen stain is a staining technique discovered by Robert Feulgen and used in histology to identify chromosomal material or DNA in cell specimens. It depends on acid hydrolysis of DNA.

DNA replication is a biological process in which two identical copies of DNA are formed from one original DNA molecule. Numerous enzymes are involved in this process such as DNA polymerase, primase, ligase, helicase, etc. Helicase enzyme unwinds double stranded DNA molecule and forms replication fork. Primase is an enzyme which is used to form RNA primer. It is a starting point for DNA synthesis. Polymerase is involved in synthesis of nucleotide by using one strand of DNA as template. Ligase is an enzyme which is used to join the two Okazaki fragments of DNA.

Watson-Crick Structure of DNA is a double-stranded, helical molecule consisting of two sugar-phosphate backbones on the outside, held together by hydrogen bonds between pairs of nitrogenous bases on the inside. In the paper "A Structure for Deoxyribose Nucleic Acid." written by j.D.Watson and F.H.C. Crick, they proposed the double helix structure of DNA. Further, in the paper, they expressed the exciting aspect of specific pairing as the key aspect of the structure in their own words-"It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for genetic material".

• DNA replication is semi-conservative in nature. When the parental strand has radioactive thymine, the daughter DNA molecule will have one strand with radio active thymine whereas the other strand will have non-radioactive thymine. 
• Thus, when it again replicates, one set of daughter molecules will have radioactive thymine, but the other won't have it completely and so on. 
• Thus, after 3 generations, we can get 2 molecules with radioactive thymine.
  

Solution
Correct answer is option A.
Explanation for correct option:

• Antisense technology is used to control the expression of a gene whose nucleotide sequence is known. 
  
• It is a form of treatment for genetic disorders or infections. 
• When the genetic sequence of a particular gene is known to be causative of a particular disease, it is possible to synthesize a strand of nucleic acid that will bind to the messenger RNA produced by that gene and inactivate it, effectively turning that gene "off".
• This is because mRNA has to be single-stranded for it to be translated. Alternatively, the strand might be targeted to bind a splicing site on pre-mRNA and modify the exon content of an mRNA.

B-DNA contains approximately 10 base pairs per coil, so 20 coils contain 200 base pairs. 120 adenine molecules correspond to 120 A-T base pairs. Number of G-C base pairs is 200-120=80.
Pyrimidine nucleotide forming 3 hydrogen bonds is cytidine monophosphate, so number of cytosine molecules is 80.

If the percentage of cytosine is 18% the percentage of thymine will be 32%. Thus, Guanine also constitutes the same percentage as that of cytosine, that is 18%. Thus, the percentage of adenine is 32%. This follows Chargaff's rule:
A+G = C+T.