Final answer:
Genetics is concerned with heredity and variation, and it was fundamentally shaped by the work of Gregor Mendel who established the principles of inheritance before the discovery of genes and chromosomes. The correct option is d. heredity and variation
Step-by-step explanation:
Genetics is the branch of biology that deals with heredity and variation. This field was pioneered by Johann Gregor Mendel, who used methodical experiments with pea plants to uncover the basic principles of genetics, even before the discovery and understanding of chromosomes, genes, and meiosis.
It is now understood that genes, carried on chromosomes, are the basic functional units of heredity capable of being replicated, expressed, or mutated.
Through Mendel's work, important concepts such as dominant and recessive traits, and the 3:1 ratio observed in the F2 generation of his experiments, were first described. These principles form the basis of Mendelian genetics, which is a great starting point for understanding inheritance. The correct option is d. heredity and variation