Why don't siblings look exactly alike?

Accualy some do, but that's a little rare, so I'm guessing because each child gets some of there mom and dad's to genetics, one child might get some of there mom's but more of there dad's and the other might get some of there dad's and more or there mom's..? not sure if that makes any sense-

they both go up but then go back down. they both end lower than they started. lastly, they both are competitive/the second on.

explanation:

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.