Where did you get your pairs of genes?
You got your 70,000 pairs of genes when your dad's sperm pierced your mom's egg. One gene from each pair of your mother's 70,000 pairs of genes was already waiting in the human egg. Your father's sperm added one gene from each of his 70,000 pairs of genes. Your father's and your mother's genes paired with each other inside that fertilized egg cell from which you then grew.
The original egg cell split and re-split, forming new cells for muscle, brain, skin, bone and all the rest of your body. These new cells came together (according to the genes' orders) and each new cell carried copies of the original cell's genes. The result: Two copies (a pair) of about 70,000 genes are found in each of the 100 trillion or so cells of your body. (That's a lotza mozzarella!)
The mix of genes you each got from your parents directs your growth to adulthood and old age. When you have children, you, in turn, pass a copy of one or the other of each pair of your genes to each of your kids - but not always the same one of the pair. Your husband or wife will do the same. Each child is very likely to get a different mix and be different from the others.
Even brothers and sisters (unless they are identical twins) don't get the same mix of genes from their parents. So, although they may have similar noses or hair or height, their bodies in other ways will be different and may react differently - less or more - to the sun, to tobacco, alcohol, or to some chemicals in bug killers or other products at home, school, or work.