With reference to the recent developments in science, which one of the following statements is not correct?
Answer & explanation
Answer: (a) Functional chromosomes can be created by joining segments of DNA taken from cells of different species.
UPSC's official answer: (a) · the answer UPSC accepted, and the one that counts in the exam
What we believe: no option fits strictly
- Statements (b), (c) and (d) are textbook techniques: recombinant DNA 'created in vitro', PCR copying DNA 'in vitro', and cell culture. By elimination (a) is the only candidate, which is how UPSC's key arrives at it.
- But (a) is also an established fact. A yeast artificial chromosome (YAC) joins yeast centromere, telomere and origin sequences to DNA from another organism, and the yeast cell copies the construct as a chromosome: 'as the yeast cells grow and divide, they amplify the YAC DNA' (NHGRI).
- NCERT itself names YACs as working vectors of the Human Genome Project: 'the vectors were called as BAC (bacterial artificial chromosomes), and YAC (yeast artificial chromosomes)'. A chromosome built from yeast and foreign DNA that replicates in a cell is a functional chromosome made from the DNA of different species.
- On a strict reading none of the four statements is incorrect; UPSC's key stands by elimination, treating (a) as the overstatement.
UPSC's key marks (a), and in the exam (a) is the option to mark, since the other three are familiar textbook techniques. Exam lesson: when three options are standard textbook facts, the fourth, least familiar claim is the one UPSC will mark.
- NIH National Human Genome Research Institute, Talking Glossary: Yeast Artificial Chromosome (YAC) ↗“Yeast artificial chromosome (YAC) is a human-engineered DNA molecule used to clone DNA sequences in yeast cells. YACs are often used in connection with the mapping and sequencing of genomes.”
- NIH National Human Genome Research Institute, Talking Glossary: YAC, how the construct replicates in yeast ↗“The YACs, with their inserted DNA, are then taken up by yeast cells. As the yeast cells grow and divide, they amplify the YAC DNA”
- NCERT Class 12 Biology, Ch 5 Molecular Basis of Inheritance (Human Genome Project) ↗“The commonly used hosts were bacteria and yeast, and the vectors were called as BAC (bacterial artificial chromosomes), and YAC (yeast artificial chromosomes).”
This box is Minimalist IAS's analysis, with its sources; it does not change UPSC's answer.
UPSC's key treats statement (a) as the one that is not correct. Statements (b), (c) and (d) each name an established laboratory technique: recombinant DNA made in vitro, copying of DNA outside a cell by PCR, and plant and animal cell culture. Statement (a) claims more, that a working chromosome is created simply by joining DNA pieces from different species; the key treats that as an overstatement, since such splicing yields recombinant DNA, a molecule, not by itself a functioning chromosome.
- ✓ (a) UPSC's key marks this as the statement that is not correct. The key's reading: joining DNA segments from different species is the making of recombinant DNA, whereas a functional chromosome is an organised structure of DNA and proteins with its own origins, centromere and telomeres, and a splice of foreign DNA is not treated as creating one. By elimination too, (a) is the only candidate, since the other three are textbook techniques.
- ✗ (b) This statement is true. NCERT describes recombinant DNA, a new combination of DNA made in vitro by joining cut DNA pieces with the enzyme DNA ligase.
- ✗ (c) This statement is true. In the polymerase chain reaction (PCR), multiple copies of a DNA segment are synthesised in vitro, that is, outside a living cell.
- ✗ (d) This statement is true. Plant and animal cells can be grown outside the body in a nutrient-rich medium, where they grow and multiply; this is cell culture.
Remember · Lab techniques that are real: recombinant DNA (joined in vitro), PCR (copying DNA outside cells) and cell culture (cells dividing in dishes). UPSC's key treats 'creating a functional chromosome by splicing DNA from different species' as the overstatement.
📘 Read it in NCERT: Class 12 Biology, Ch 9 (practise this chapter) · Class 12 Biology, Ch 9 (practise this chapter) · Class 9 Exploration, Ch 2 (practise this chapter) · Class 12 Biology, Ch 5 (practise this chapter)
Sources
- NCERT Class 12 · Biology, Chapter 9 “This makes a new combination of circular autonomously replicating DNA created in vitro and is known as recombinant DNA.”
- NCERT Class 12 · Biology, Chapter 9 “PCR stands for Polymerase Chain Reaction. In this reaction, multiple copies of the gene (or DNA) of interest is synthesised in vitro”
- NCERT Class 9 · Exploration, Chapter 2 “Scientists have developed methods to grow plant and animal cells outside the body in special conditions. This is called cell culture.”
- NCERT Class 12 · Biology, Chapter 5 “The commonly used hosts were bacteria and yeast, and the vectors were called as BAC (bacterial artificial chromosomes), and YAC (yeast artificial chromosomes).”
- NIH National Human Genome Research Institute, Talking Glossary: Yeast Artificial Chromosome (YAC) ↗ “Yeast artificial chromosome (YAC) is a human-engineered DNA molecule used to clone DNA sequences in yeast cells.”
Question and answer: UPSC's official GS Paper I (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). ·