As often happens with me, the harder I work on one thing, the more I get really interested in some completely unrelated distraction. My CTIX colleague Robert Horton refers to this as "dynamic shirking".
However, there were a few starting points. First, I have been noticing all the wonderful similarities and differences between my two daughters, and how they compare to Nissa and I. Besides the straightforward one-to-one inheritance of features (who's nose does she have), I was noticing some of what appeared to me to be quantitative variation (although I have not actually measured anything). This first hand experience got me thinking,"How does this whole inheritance thing really work?"
I realized that there were some very fundamental things I didn't have answers for.
Also I was reading through your Glossary post recently, and that got me thinking too.