It indicates what elements is composed by and how many atoms of one element are linked to the other.
For example, this is the formula for table salt is:
NaCl
The formula indicates that table salt (sodium chloride) is composed by sodium (Na) and chlorine (Cl) on a 1:1 ratio.
Hope it helped,
BioTeacher101
B. Gene. Piebalding is caused by mutant copies of genes.
ANSWER: C. Complementary base pairing occurs only between the probe and the target gene.