Question of the Day – Extrachromosomal DNA
QOTD March 11,2026
With reference to Extrachromosomal DNA (ecDNA), consider the following statements:
- ecDNA refers to circular fragments of DNA that exist outside the main chromosomes in the cell nucleus.
- ecDNA often carries multiple copies of oncogenes that can accelerate tumour growth.
- ecDNA inheritance always follows the classical Mendelian law of independent assortment.
Which of the statements given above is/are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 only
(d) 1, 2 and 3
Answer: (a) 1 and 2 only
Explanation:
Statement 1-Correct
Extrachromosomal DNA (ecDNA) consists of small circular DNA fragments that exist separately from chromosomes in the cell nucleus. It originates when pieces of chromosomal DNA break away due to damage or replication errors.
Statement 2-Correct
ecDNA frequently contains multiple copies of oncogenes, which are genes that promote cancer growth. This amplification increases gene activity and helps tumours grow faster and become more aggressive.
Statement 3-Incorrect
ecDNA does not follow Mendelian inheritance rules. Instead of random segregation like chromosomes, ecDNA can be inherited as clusters, preserving advantageous gene combinations in cancer cells.
Why in news–
The discovery of Extrachromosomal DNA (ecDNA) has been in the news after recent scientific studies reported in The Hindu highlighted how ecDNA may challenge traditional principles of genetics established by Gregor Mendel. Researchers found that ecDNA consists of small circular DNA fragments that exist outside normal chromosomes within the cell nucleus and are commonly found in many cancer cells. These fragments often carry multiple copies of oncogenes that promote tumour growth and drug resistance. Unlike genes located on chromosomes, which follow Mendel’s law of independent assortment, ecDNA can be inherited together in clusters during cell division, allowing cancer cells to preserve advantageous gene combinations. This discovery is significant because it provides new insights into cancer progression and treatment, and could lead to the development of targeted therapies against ecDNA-driven cancers.
News-ecDNA challenges law of genetics, groundbreaking new studies find – The Hindu
There are more questions from this topic that you should practice to make your concepts stronger.
Practice Questions (PQ)
PQ1. With reference to Extrachromosomal DNA (ecDNA), consider the following statements:
- ecDNA can move freely within the nucleus of the cell.
- ecDNA is found only in bacterial cells and not in human cells.
- ecDNA plays a role in tumour evolution and drug resistance.
Which of the statements given above is/are correct?
(a) 1 and 3 only
(b) 1 only
(c) 2 and 3 only
(d) 1, 2 and 3
Answer: (a)1 and 3 only
Explanation
Statement 1-Correct
ecDNA is not attached to chromosomes and can move freely within the cell nucleus, forming clusters that increase gene expression.
Statement 2-Incorrect
ecDNA occurs in eukaryotic cells including human cancer cells, not only in bacteria.
Statement 3-Correct
ecDNA contributes to tumour evolution, oncogene amplification, and resistance to chemotherapy, making cancers harder to treat.
PQ2. With reference to the laws of inheritance proposed by Gregor Mendel, consider the following statements:
- The Law of Segregation states that each parent passes only one allele for a trait to offspring.
- The Law of Independent Assortment states that genes located on different chromosomes are inherited independently.
- ecDNA inheritance strictly follows Mendel’s Law of Independent Assortment.
Which of the statements given above is/are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 only
(d) 1, 2 and 3
Answer: (a)1 and 2 only
Explanation:
Statement 1-Correct
The Law of Segregation states that during gamete formation, the two alleles of a gene separate so each gamete receives one allele.
Statement 2-Correct
The Law of Independent Assortment states that genes for different traits are inherited independently when they are located on different chromosomes.
Statement 3-Incorrect
ecDNA violates Mendelian inheritance patterns because its gene clusters can be inherited together rather than independently.
PQ3. Consider the following statements regarding DNA in human cells:
- Most DNA in human cells is located in chromosomes inside the nucleus.
- ecDNA is a type of DNA found outside chromosomes but still within the nucleus.
- ecDNA is always present in all normal healthy cells.
Which of the statements given above is/are correct?
(a) 1 and 2 only
(b) 2 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer: (a) 1 and 2 only
Explanation:
Statement 1-Correct
Human genetic material is mainly organised in 23 pairs of chromosomes inside the nucleus.
Statement 2-Correct
ecDNA exists outside chromosomes but still within the nucleus, functioning separately from chromosomal DNA.
Statement 3-Incorrect
ecDNA is commonly found in cancer cells and is rare or absent in most normal healthy cells.
Previous Year Question (UPSC Prelims)
With reference to genome editing, consider the following statements:
- Genetic changes can be introduced in the cells that produce eggs or sperms of a prospective parent.
- A person’s genome can be edited before birth at the early embryonic stage.
- Human-induced pluripotent stem cells can be injected into the embryo of a pig.
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 and 3 only
(c) 2 only
(d) 1, 2 and 3
Answer: (d) 1, 2 and 3
Explanation
Statement 1-Correct
Genome editing techniques such as CRISPR-Cas9 can modify genes in germ cells (sperm or egg cells), allowing the changes to be inherited by future generations.
Statement 2-Correct
Genome editing can be applied at the early embryonic stage, allowing modification before birth.
Statement 3-Correct
Scientists can insert human-induced pluripotent stem cells into animal embryos (e.g., pigs) for research such as organ development studies.
