Explanation

Genetic screening is the testing of a person's DNA to detect the presence of a particular gene or genetic marker associated with a disease or trait, typically before symptoms appear (e.g., screening for thalassemia or cystic fibrosis carriers). It is an analysis of the individual's DNA, not of genes across a whole population, which rules out option B (population genetics). Pedigree analysis (C) merely traces inheritance patterns within families, and infertility screening of parents (D) is a different clinical test altogether. Hence the definition in option A is correct.