Rather than concentrate on how many generations of yeast it takes to mutate etc, I think a bigger factor for home-brewers is maintaining the yeast in a safe, sanitary and pure form - we are not a chemistry/biology lab so there will always be a level of infection where we introduce unwanted wild yeasts, bacteria and other bugs into our 'farmed' samples - especially if re-using the trub. So I'd suggest those factors would be as much of a limitation compared to genetic mutations over generations.
Of course many breweries have (and still do) reuse and repitch their yeast generation after generation (and some have for 100's of years), however in those situations they are brewing (and breeding) the yeast in exactly the same conditions every time, so the yeast is propagated according to those specifications - again this is not something that is possible on a home-brewing scale.
Of course many breweries have (and still do) reuse and repitch their yeast generation after generation (and some have for 100's of years), however in those situations they are brewing (and breeding) the yeast in exactly the same conditions every time, so the yeast is propagated according to those specifications - again this is not something that is possible on a home-brewing scale.
