What scientific field focuses on the study of heredity and variation in organisms?

The field that focuses on the study of heredity and variation in organisms is genetics. Genetics is a branch of biology that deals with the principles of heredity and variation among living organisms. It explores how traits are passed from parents to offspring through genes, the units of heredity. This includes the study of genetic variation within populations and how these variations contribute to the evolution and adaptation of species over time.

Other options, while being significant scientific disciplines, do not align with the study of heredity and variation in organisms. Geology is concerned with the Earth's physical structure and substance, geophysics focuses on the physical processes and properties of the Earth, and botany is the study of plants, which may include genetic aspects but is not exclusively focused on heredity as a central theme. Hence, genetics is the domain directly related to understanding how organisms inherit characteristics and how those characteristics can vary.