In humans there are 23 pairs of chromosomes, or 46 single chromosomes in all cells of the body except the sex cells. Autosomes are regular body cells , reproduce using Mitosis , or asexual reproduction. 1 cell becomes 2 new cells. Gamete cells the sex cells reproduce using Meiosis or sexual reproduction. 1 cell becomes 4 new cells.
Genes are the smallest chemical parts that form segments of chromosomes.
Genes determine what we look like. There are not two organisms alike in the world unless you are an identical twin or a clone. Alleles are an alternate form of a gene for one trait. E.g. Brown and blue eyes are two different alleles for eye color. We have 2 alleles for any, one trait, one from our mother and one from our father.