How does DNA explain both the unity and diversity of life?

A: Scurvy is a disease caused by a vitamin C deficiency

B: the way these genes are selected for or against in nature to increase the reproductive survival (or fitness) of a population is NOT at all random

C: genetic disease caused by a mutation in the genes that code for the enzymes that either stabilize or make collagen.

D: unity in that there are only four nucleotides that makes every single organisms DNA but they way they can be sequenced is diffrent