Question

Assertion (A): The human embryonic stem cells can be derived from the inner cell mass of blastocyst and cultured in a suitable nutrient medium.
Reason (R): It is possible to selectively remove a gene and make precise genetic modification in mouse embryonic stem cells.

• A. Both Assertion (A) and Reason (R) are true and the Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but the Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

Embryonic stem cells are pluripotent, meaning they can differentiate into cells of all three germ layers: ectoderm, mesoderm, and endoderm. They cannot, however, form extra-embryonic tissues like the placenta.

Answer 1

The Correct Option is B

Step 1: Evaluating the Assertion (A)
Embryonic stem cells (ESCs) are pluripotent stem cells. In humans, pluripotent embryonic stem cells are routinely isolated from the inner cell mass (ICM) of a 5-day-old blastocyst and cultured in vitro under sterile conditions on mouse embryonic fibroblast feeder layers. Thus, Assertion (A) is true.

Step 2: Evaluating the Reason (R)
In genetic engineering, homologous recombination techniques are used in mouse embryonic stem cells to selectively delete ("knock out") or modify specific genes, enabling the generation of transgenic mouse models. Thus, Reason (R) is true.

Step 3: Analysis of Correlation
While both statements are scientifically correct, the ability to knock out a gene in mouse embryonic stem cells (R) is a technological method used for animal transgenesis. It does not explain the biological fact of how or where human embryonic stem cells are derived and cultured (A). The two statements are independent facts within stem cell biology.

Step 4: Conclusion
Hence, both A and R are true, but R is not the correct explanation of A, matching option (B). Final Answer: (B)