I was using that as kind of an extreme example, because it takes 20 generations of brother/sister matings to create a fully inbred mouse model, but even a few generations of inbreeding will create a pretty high coefficient of inbreeding.
There’s equations to calculate heterozygosity/homozygosity based on inbreeding coefficients so you could sit down and calculate after how many generations what % of the genome is likely to be homozygous (this is generally a bad thing), I just don’t have it in me to do it right now. Population genetics is not my favorite 