Q.36 Determine the correctness or otherwise of the following Assertion (a) and the Reasonv[r].
Assertion [a]: Embryonic stem cells are suitable for developing knockout mice
Reason [r]: Homologous recombination is more frequent in embryonic stem cells than that in somatic cells
(A) Both [a] and [r] are false
(B) Both [a] and [r] are true, and [r] is the correct reason for [a]
(C) Both [a] and [r] are true, but [r] is not the correct reason for [a]
(D) [a] is true, but [r] is false

Embryonic Stem Cells in Knockout Mice: Assertion-Reason Analysis

Embryonic stem (ES) cells enable knockout mouse production through targeted gene disruption. The assertion and reason both hold true, with the reason directly explaining the assertion’s validity.

Assertion [a] Evaluation
Assertion [a] states that embryonic stem cells are suitable for developing knockout mice. This holds true because ES cells, derived from early mouse embryos, maintain pluripotency, allowing genetic modifications via homologous recombination in culture followed by injection into blastocysts to form chimeras that transmit the mutation germline. Somatic cells lack this capability due to differentiation, making ES cells uniquely ideal for precise gene knockouts.​

Reason [r] Evaluation
Reason [r] claims homologous recombination occurs more frequently in ES cells than somatic cells. This is correct, as ES cells exhibit elevated homologous recombination efficiency compared to differentiated somatic cells, facilitating rare targeted integration events essential for knockouts. Lower rates in somatic cells render them impractical for standard knockout protocols.​

Option Analysis

• (A) Both false: Incorrect, as both [a] and [r] are true based on established protocols.​

• (B) Both true, [r] correct reason for [a]: Correct, since higher homologous recombination in ES cells directly enables their suitability for knockouts.​

• (C) Both true, [r] not reason: Incorrect, as recombination efficiency is the key mechanistic reason.​

• (D) [a] true, [r] false: Incorrect, as [r] accurately reflects biological fact.​

Correct Answer: (B)

Introduction: Unlocking Knockout Mice with Embryonic Stem Cells and Homologous Recombination
Embryonic stem cells revolutionize knockout mice creation through efficient homologous recombination, a core technique in genetic research. This article dissects an IIT JAM assertion-reason question on embryonic stem cells knockout mice suitability, explaining why both statement and reason align perfectly for option (B).

What Makes Embryonic Stem Cells Ideal for Knockout Mice?
Embryonic stem cells derive from blastocysts and retain pluripotency, enabling culture expansion post-genetic targeting. Targeting vectors integrate via homologous recombination, disrupting specific genes, then modified ES cells produce chimeric mice that breed true knockouts. Unlike somatic cells, ES cells support germline transmission critical for heritable models.​

Homologous Recombination: Higher in ES vs Somatic Cells
Homologous recombination frequency surges in undifferentiated ES cells versus somatic cells, boosting targeting success from <10^-6 to viable levels. Somatic cells favor non-homologous end joining, reducing precision. This efficiency underpins ES cell use in knockouts.​

Detailed Assertion-Reason Breakdown for Exam Success

• Assertion true: ES cells proven for knockouts since 1980s protocols.​

• Reason true: Recombination 10-100x higher in ES cells.​

• Link: Frequency directly causes suitability (option B).​

Exam Tips: Assertion-Reason Strategies
Master by verifying each part independently, then causal link. Practice recalls ES cell protocols for biotech entrances.​