**Core Concept:** Population genetics is the study of genetic variation within a species and how it changes over time and across populations. It involves analyzing genetic diversity, gene flow, mutation, and natural selection to understand how populations evolve.

**Why the Correct Answer is Right:** The correct answer (D) refers to the founder effect, a significant event in population genetics. The founder effect occurs when a small number of individuals from one population settle in a new area and establish a new population. Due to genetic drift, the genetic variation in the new population may differ significantly from the original population.

**Why Each Wrong Option is Incorrect:**

A. **J.B.S. Haldane (1901-1984)**: An eminent British biologist, geneticist, and mathematician, Haldane made significant contributions to genetics and population genetics. However, the question refers to the person who introduced the concept, not a specific contribution.

B. **Wright's (Sewall Wright) Shifting Balance Theory**: This theory explains how natural selection acts on populations, but it doesn't address the specific population genetic event described in the question.

C. **Mendel's Laws of Inheritance**: Gregor Mendel (1822-1884) is famous for his laws of inheritance, which describe how traits are passed from parent to offspring. Mendel's work laid the groundwork for modern genetics, but the question asks for the person who introduced the concept of the founder effect.

**Clinical Pearl:** Understanding population genetics helps in understanding genetic disorders, disease susceptibility, and evolutionary dynamics. In clinical practice, it can aid in predicting genetic traits and consanguineous marriages, which might increase the risk of genetic disorders in offspring due to inbreeding.

**Correct Answer:** D. J.B.S. Haldane (1901-1984) introduced the concept of the founder effect in population genetics. The founder effect is a significant event in population genetics, which highlights the importance of genetic drift in shaping a population's gene pool. This concept is crucial for understanding genetic disorders, migration, and genetic diversity.