Genetics

It’s thought that genetics are received from parents in sort of a blend, like red paint from the mother and green paint from the father.

consider the absurdity of this, since if every child was some combination of their parents, then every child would have a hair color that is the color of their parents', would have a skin tone that is between their parents', and would be hermaphodites.
instead of a blend, it’s more like a deck of cards which is composed of cards contributed by both parents.
any one of your sperms (or eggs if female) contains your fathers version of a particular gene or your mother’s version; not a blend of the two.
- and that particular gene came from one (and only one) of your grandparents, and so on.

At any one time, the genes within a population (say, rats) are all sitting in the bodies of individual rats, or they are moving into new rat bodies via sperms

taking a long view across many generations on an isolated island, we see all the rat genes on the island being mixed up as though they were cards in a single well-shuffled pack: one single pool of genes.
Each animal in a population is a sampling of the gene pool of its time (or rather, its parents' time). There is no intrinsic tendency in gene pools for particular genes to increase or decrease in frequency. However, when there is an increase/decrease in how frequently a specific gene occurs, that is what is meant by evolution.

Height is somewhere between 60-80% determined by a person’s genes. However, consider that environment can potentially play a big part in the outcome of a person's height. Consider that even if a person was predisposed to being tall, if they were malnourished and thus unable to grow at a regular rate as permitted by those genes, they would not reach the height as they would have prescribed.

When genetics are identical, any differences you see must be due to the environment. When the environment is identical, then any differences must be due to the genetics.

A widespread genetic phenomenon called pleiotropy exists, whereby seemingly unconnected traits come along for the ride when other “main” traits are selected (whether natural or artificial)

ex. In breeding for tameness, foxes were found to exhibit many of the same traits as dogs. They had curly tails and floppy ears. It’s not that they were bred for these features. They were only bred for tameness, but these other traits came along for the ride.
This illustrates a generally important point about evolution. When you notice a characteristic of an animal and ask what its Darwinian survival value is, you may be asking the wrong question. It could be that the characteristic you have picked out is not the one that matters.

Children