The main difference between the four nucleotides that make up DNA is that they have different sugars.

uracil.

bonds.

bases.

the answer is sugars

Explanation:

The basic building block of DNA is called a NUCLEOTIDE. A nucleotide is made up of one sugar molecule, one phosphate molecule and one of the four bases. Note that the purine bases (adenine and guanine) have a double ring structure while the pyrimidine bases (thymine and cytosine) have only a single ring.

✿   this landform has a high elevation and a high relief

✿   this landform is a mountain

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).