**Core Concept**
Pharmacokinetics is the study of how a drug is absorbed, distributed, metabolized, and eliminated (ADME) in the body. This branch of pharmacology focuses on the time course of drug concentrations in the body, which is crucial for understanding the efficacy and toxicity of medications.

**Why the Correct Answer is Right**
Pharmacokinetics involves the study of various processes, including absorption from the site of administration (e.g., gastrointestinal tract, skin), distribution to different tissues and organs, metabolism by enzymes (e.g., cytochrome P450), and elimination through excretion (e.g., kidneys, liver). Understanding these processes is essential for predicting drug concentrations, optimizing dosing regimens, and minimizing adverse effects. Pharmacokinetics also considers factors that influence drug movement, such as age, sex, weight, and renal or hepatic function.

**Why Each Wrong Option is Incorrect**
**Option B:** The study of drug effects is actually pharmacodynamics, which examines the biochemical and physiological effects of drugs on the body.

**Option C:** Pharmacogenetics, not pharmacokinetics, is the study of how genetic variations affect an individual's response to drugs, which is indeed influenced by heredity.

**Option D:** Pharmacokinetics is indeed one of the above, specifically the study of drug movement in the body.

**Clinical Pearl / High-Yield Fact**
Pharmacokinetic parameters, such as half-life and clearance, are essential for optimizing drug therapy. For example, a drug with a long half-life may require less frequent dosing, while a drug with a short half-life may require more frequent dosing to maintain therapeutic concentrations.

**✓ Correct Answer: A. Study of drug movement in the body**