Answer:
Genetics.
Step-by-step explanation:
Genetics may be defined as the branch of biology that deals with the study of the heredity and variations in the living organisms. Mendel is known as the father of genetics.
The genetics explains the inheritance of a particular trait and the factors that can affect the trait. The expression of the trait and its influence in the environment can also be measured by genetics. The linkage and transmission of sex linked characters is also studied in genetics.
Thus, the correct answer is option (A).