Answer: The correct answer is -
Genes.
Gregor Mendel worked with pea plants in order to find out the inheritance pattern of certain traits from parents to their next generation.
He proposed that for every characteristic in an organism, there are two basic factors (inherited from each parent).
These factors/units were later called genes (which are considered as unit of heredity) and are located on chromosomes.
Genes can be described as the segment of DNA that codes for a particular trait /characteristic of an organism.
For example - 'T' and 't' gene correspond to tall and dwarf height of pea plant respectively.
Thus, gene is the right answer.