CBSE Questions for Class 12 Medical Biology Molecular Basis Of Inheritance Quiz 13 - MCQExams.com

• DNA fingerprinting also called DNA typing, DNA profiling, genetic fingerprinting, genotyping, or identity testing, in genetics is a method of isolating and identifying variable elements within the base-pair sequence of DNA (deoxyribonucleic acid). 
• DNA fingerprinting is currently used both for identifying paternity or maternity and for identifying criminals or victims.

• The Human Genome Project (HGP) is an international scientific research project with the goal of determining the sequence of chemical base pairs which make up human DNA and of identifying and mapping all the genes of the human genome from both a physical and functional standpoint. 
• It remains the world's largest collaborative biological project. 
• The US government proposed and funded the project; planning started in 1984, the project got underway in 1990 and was declared complete in 2003. 
• The DOE, European Commission, and the NIH established working groups to address genome mapping, computational analysis to handle databases, and the social, legal, and ethical implications of human genome research.

Correct answer: option (B)

Explanation for the correct option: (B)

• A codon is a triplet and encodes a specific amino acid.
  They never overlap.This leads to 4 codons in the mRNA  AUGGCAGUGCCA . the codons are AUG-GCA-GUG-CCA i.e., 4.
• But in the question, it is assumed that they are overlapping. This means that each nucleotide initiates a codon. 
• This leads to a total of 10 codons in the mRNA sequence AUGGCAGUGCCA as AUG, UGG, GGC, GCA, CAG, AGU, GUG, UGC, GCC, CCA. 

Correct Option: C
Explanation:

• The genetic code consists of 64 (4^3) triplets of nucleotides.
• These triplets are called codons. With three exceptions, each codon encodes for one of the 20 amino acids used in the synthesis of proteins.
• That produces some redundancy in the code: most of the amino acids being encoded by more than one codon. 
• So, if evolution on earth has occurred in such a way that there are 96 amino acids instead of 20.
• DNA has 12 different types of bases and DNA synthesis occur in the same way as today.
• The minimum number of bases per DNA codon would be 2 (12^2=144) all the time.

• Promoter sequences are DNA sequences in the region in the gene where the RNA polymerase will bind and initiate the process of transcription. 
• They are located upstream at the 5' end of the transcription initiation site in the structural gene. 
• Promoter sequences define the direction of transcription and indicate the DNA strand that will be transcribed. 
• The strand which is from 5'-3' is the non-template strand and the strand which runs from 3'-5' is known as the template strand. 

A) Correct option A
B) Explanation of the correct option

• The genetic code is degenerate which means that most amino acids are specified by more than one codon.
• As we know that there are only four nucleotides namely deoxyadenosine, deoxyguanosine, deoxythymidine and deoxycytidine.
• Further, there are 20 essential amino acids that are to be encoded by these four nucleotides.
• A triplet code could make a genetic code for 64 different combinations (4 X 4 X 4) genetic code.
• Thus, there are ample codons to specify 20 amino acids. 

Correct Option: A
Explanation:

• Nucleotides comprise a nitrogenous base, a pentose sugar and a phosphate. 
• The molecule without the phosphate group is called a nucleoside. 
• Deoxyadenosine, deoxyguanosine, deoxycytidine are few examples of nucleosides while adenylate, guanylate, uridylate, cytidylate are few examples of nucleotides. 
• Hence, a nucleoside is a nitrogenous base + sugar.

• A non-protein chemical that is necessary for the activity of protein/enzyme is known as a co-factor. 
• Mg$$^{2+}$$ serves as co-factor for DNA polymerase. It activates the DNA polymerase that is used to synthesise the DNA during replication.
• Thus, the correct answer is B.

• RNA polymerase helps in DNA dependent RNA synthesis. This process is known as transcription. DNA strands are used as a template to synthesize RNA molecules.
  
• DNA ligase is used to join DNA segments during DNA repair or during replication (to join Okazaki fragments of the lagging strands).
  
• DNA polymerase works in the pair to synthesis new strand for DNA molecule from deoxyribonucleotides. In other words, it helps in DNA dependent DNA synthesis.
  
• Topoisomerase enzyme participates in overwinding or unwinding of DNA. During DNA replication or transcription, DNA becomes overwound ahead of the replication fork. It binds to DNA and cut the phosphate backbone of either one or both the DNA strands.