Answer: The correct answer is -
D. They determine the inherited traits of an organism.
Gene can be described as segment of DNA (deoxyribonucleic acid) that codes for particular protien, which determines specific trait (which is an inherited trait) of the organism.
Genes are located on chromosomes as considered as the unit of heredity as they are passed from one generation to the next generation.
Examples for inherited trait include eye color, skin color, hair shape and color etc.
Thus, option D) is the right answer.