Give an example of what would happen if the diploid number was not reduced to haploid before fertilization.

Haploid cells are cells that composed of only one complete set of chromosomes. The very common type of haploid cells is gametes, or sex cells. Haploid cells are produced by meiosis. They are genetically diverse cells that are used in sexual reproduction. In humans, the haploid cells have 23 chromosomes, versus the 46 in the diploid cells.  When the parent donor gives fertilized haploid cells, the offspring has a complete set of chromosomes and becomes a diploid cell. A haploid cell with have a haploid number, which is the number of chromosomes found within the nucleus that create one set. 

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.