He is an expert in pathology.

He is an expert in immunology.

He is an expert in ichthyology and has a deep knowledge of marine life.

He is an expert in anthropology.

He is an expert in virology.

He is good at solving algebra problems.

He is majoring in political science at university.

He has a deep interest in teratology.

I am majoring in embryology at university.

He is an expert in embryology, studying the developmental processes of many kinds of organisms.