In the ladder analogy of the DNA molecule, the "steps of the ladder are Sugars
O Joined sugar and phosphate
O Paired nitrogen bases

haploid cells;

the correct answer is:

a population changes in response to a change in the environment.

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.