What does the term atomic mass mean

Atomic mass in can be defined as:

The mass of an isotope of an element measured in units formerly based on the mass of one hydrogen atom taken as a unit

Hope this helped :3

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