All Free Biology MCQs with Answers

• A. Gel electrophoresis
• B. DNA finger printing
• C. Polymerase chain reaction
• D. Recombinant DNA technology

Explanation: Polymerase Chain Reaction (PCR) is a method used to amplify DNA sequences, usually visualized with thermocyclers and reagents. As shown in figure, option C is correct. All other options don't involve DNA amplification. So A,B and D are wrong.

• A. Karyotyping
• B. Amplification of a gene
• C. Isolation of genes from organism
• D. Synthesis of insulin from bacteria

Explanation: The correct answer is synthesis of insulin from bacteria. The universality of the genetic code means that the same codons code for the same amino acids across different organisms. This allows a gene from one organism, such as the human insulin gene, to be inserted into another organism, such as a bacterium, and be expressed correctly. This is the basis for producing human insulin in bacteria, which is a common practice in biotechnology.Other options are incorrect because they do not rely on the universality of the genetic code. Karyotyping is a method for organizing and studying chromosomes, gene amplification is a technique to increase gene copies, and gene isolation is a basic molecular biology procedure. None of these directly benefit from the genetic code being universal.

• A. Suspect 1
• B. Suspect 2
• C. Suspect 3
• D. Suspect 4

Explanation: The correct answer is Suspect 3. The DNA fingerprints collected from the crime scene match exactly with the DNA pattern of Suspect 3, confirming their involvement. The other suspects' DNA patterns do not align with the forensic evidence, ruling them out as potential matches.

• A. Clone a DNA fragment
• B. Isolate a gene from the bacterium
• C. Detect the presence of mutation in a gene
• D. Search for a certain gene in a genetic library

Explanation: The correct answer is Option D: DNA probes are used to search for a certain gene in a genetic library. DNA probes are short, labeled, single-stranded sequences of DNA that hybridize to complementary sequences in the genome, allowing researchers to identify the presence of specific genes. Option A is incorrect because cloning involves replication rather than identification. Option B is not correct as isolation requires different techniques, though probes can aid in identification. Option C, while true in other contexts, is not the primary use of probes in genetic libraries.

• A. Hydrogen at 2nd carbon, which is required for the formation of hydrogen bond
• B. OH group at 3rd carbon, which is required for the formation of phosphodiester bond
• C. Nitrogenous base at 1st carbon, which is required for the formation of hydrogen bond
• D. Phosphate group at 5th carbon, which is required for the formation of phosphodiester bond

Explanation: In Sanger's DNA sequencing method, dideoxyribonucleotides are used to terminate DNA strand elongation. The key feature of these molecules is the absence of the 3' hydroxyl (OH) group, which is essential for forming phosphodiester bonds with the next nucleotide. Without this OH group, the DNA polymerase cannot add another nucleotide, thus terminating the chain. Option B is correct as it identifies the critical role of the 3' OH group in chain elongation.Options A, C, and D describe other structural aspects that do not contribute to the chain termination process in the context of Sanger sequencing.

• A. Option A
• B. Option B
• C. Option C
• D. Option D

Explanation: The size of a DNA molecule is inversely proportional to the distance it has traveled during electrophoresis. Option A is the correct answer because this band represents the largest DNA fragment, which has moved the least distance in the gel. It is also closer to the negative pole or end.B and C have travelled moderate distances, whereas D has travelled the greatest distance of all, making these options incorrect.

• A. Cloning
• B. Tissue culture
• C. Gene therapy
• D. Genetic engineering

Explanation: The correct technique used to transfer a gene for resistance to a toxin into a farm animal is Genetic engineering. This process involves directly manipulating the DNA of an organism to introduce new traits, such as resistance to toxins. In contrast, Cloning is about creating identical copies, Tissue culture is about growing cells in vitro, and Gene Therapy is a medical treatment focused on correcting defective genes in humans rather than transferring genes to animals.

• A. Option A
• B. Option B
• C. Option C
• D. Option D

Explanation: 5'-GCTTGC-3'3'-CGAACG-5' → reverse complement is CGAACG, which is not equal to GCTTGC → Not palindromicSo D is the correct option.

• A. Isolate the gene of interest
• B. Identify the plasmids in bacteria
• C. Synthesise the complementary DNA from mRNA
• D. Facilitate the insertion of foreign DNA into vector

Explanation: Sticky ends have short single-stranded overhangs that can form complementary base pairs with matching ends on another DNA fragment. This makes it much easier and more accurate to insert foreign DNA into a plasmid/vector.So D is the correct option. Rest of the options are incorrect.

• A. 16
• B. 32
• C. 64
• D. 128

Explanation: The polymerase chain reaction (PCR) is a process that amplifies DNA, doubling the number of molecules with each cycle. Starting with one double-stranded DNA, the first cycle produces 2 copies, the second cycle produces 4, the third produces 8, and so on. Therefore, after the 6th cycle, the number of double-stranded DNA molecules is 2^6 = 64. Option C is correct because it correctly represents this exponential growth.Option A (16) and Option B (32) underestimate the number of cycles, while Option D (128) overestimates it as it assumes an additional cycle.