**Core Concept:** Karyotyping is a laboratory technique used to examine the chromosomes of a cell to diagnose genetic disorders, abnormalities, or assess the health status of an individual. The cell cycle consists of four phases: G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis). Among these, karyotyping is performed in the M phase of the cell cycle.

**Why the Correct Answer is Right:** Karyotyping is performed in the M phase because chromosomes are visible and easily distinguishable during this phase. During the other three phases (G1, S, and G2), chromosomes are compact and invisible. Karyotyping is essential for evaluating the number, size, and structure of chromosomes, which can reveal abnormalities that may indicate genetic disorders.

**Why Each Wrong Option is Incorrect:**

A. **G1:** Chromosomes are compact and not visible, making karyotyping impossible in this phase.
B. **S:** Chromosomes are still compact and not visible, rendering karyotyping inappropriate during this phase.
C. **G2:** Chromosomes are invisible due to their compact state, making karyotyping inefficient during this phase.
D. **M:** While karyotyping is performed during the M phase, it is incorrect to say that karyotyping is only done in this phase.

**Clinical Pearl / High-Yield Fact:** Understanding the cell cycle phases helps medical students understand the appropriate timing for various diagnostic tests and procedures. For example, biopsies are typically performed during the G1 phase, while endoscopy and colonoscopy are done during the active growth phase (Phase II) of the small intestine. This knowledge helps ensure optimal timing for diagnostic tests and procedures for accurate results.

**Correct Answer:** C. M (Mitosis) - Karyotyping is performed during the M phase of the cell cycle when chromosomes are visible and easily identifiable.