AMA #50: Genetics: how they impact disease risk, what you can do about it, testing, and more

We share 99% of our DNA with chimpanzees. We share about 90% of it with cats ... We're about 50-60% genetically identical to bananas.

DNA is just a code of instructions that tell a cell how to function. So, there are lots of analogies here, but I really think that the best one is kind of thinking of it as a cookbook. So, a cookbook will have discrete sets of instructions in the form of individual recipes, and DNA also has a discrete set of instructions in the form of individual genes.

Height is about 80% heritable. So, that means it's mostly determined by genetics. But a lot of factors—i.e., 20% of that—can be determined by things such as childhood and gestational nutrition, hazardous exposures, like if the mom was smoking during pregnancy. Those can contribute to the other 20%.

Genes are sort of the same way. So, they only work by being expressed ... So, expression means making a copy of that DNA into something called RNA—that process is called transcription—and then turning that RNA into a protein, and that process is called translation.

Humans only have about 20,000 protein-coding genes in total. Maybe that sounds like a lot, but if you consider the fact that lab mice, on average, have about 23/25,000 genes...

Everyone has the same set of genes, but different individuals have small variations in the sequence of those genes or in the surrounding DNA—these are called SNPs, or single nucleotide polymorphisms—and these influence the gene's level of expression, or even the level of function of the gene's protein product.

All humans are at least 99.% genetically identical to each other.