**Core Concept**
The study of the precise genetic composition of a population and the various factors determining the incidence of inherited traits in them is a fundamental concept in genetics. This field involves the analysis of genetic variation within a population and how it affects the expression of traits.

**Why the Correct Answer is Right**
The correct answer is **Population Genetics**. This field of study focuses on the genetic makeup of a population and how genetic variation is passed down from one generation to the next. It examines the frequency and distribution of genetic traits within a population and how they are influenced by factors such as mutation, gene flow, and natural selection. Population genetics is crucial in understanding the evolution of species and the development of genetic disorders.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the study of genetic composition and inherited traits within a population.

**Option B:** This option is incorrect because it refers to the study of the structure and function of genes, rather than the population-level analysis of genetic variation.

**Option C:** This option is incorrect because it refers to the study of the genetic basis of disease, rather than the broad study of genetic composition and inherited traits within a population.

**Clinical Pearl / High-Yield Fact**
Population genetics is essential in understanding the genetic basis of common diseases and developing targeted treatments. It also helps in identifying genetic predispositions to certain conditions, allowing for early intervention and prevention.

**Correct Answer:** D. Population Genetics