We mention the term gene here but it is, for the most part, unimportant to genetic genealogy. Genes are the (known) active regions of the DNA. Most of our DNA is either junk or simply unknown function. It is known that more changes occur in the junk regions than in the gene regions. Major changes in a gene prevent the cell or organism from surviving and reproducing. SNPs and STRs can occur in junk or gene regions; albeit most (/all?) STRs seem to be in the junk region.

So DNA strands consist of junk (or inter-gene) regions and genes. Genes themselves are much more complex in that they have intro and exit regions, coding and non-coding, and the like. SNPs may occur in any region within and outside the gene. But all this structure is not important to understand genetic genealogy. Suffice it to say, the DNA strand has more important areas than others and the SNPs and STRs are scattered in and among them all.