Humans may have type O, A, B, AB blood. This blood
type is a trait that is determined by?

nucleic acid molecules are incredibly complex, containing the code that guarantees the four different nucleotide units comprise dna, the nucleic acid of interest to the genealogist. and one of four nitrogen-containing molecules called nucleotides

all matter is made up of atoms

in any element all atoms are the same

elements in a compound are always in a constant ratio: apex