Couple years ago, I read an article (I think it was linked here) about a study on chick genders relating to temps. If I recall correctly, it said that eggs that got cold were more likely to hatch pullets. Of course it didn't say how "cold" cold was. My MIL and I were getting ready to load the incubator and battling getting eggs in from the coop before they froze. Out of 27 eggs in the incubator, 20 developed, 17 hatched (3 with developemental issues)and 14 lived at least long enough to determine gender (hawk got one half grown). I think we had 5 roos out of the 14....lending some credence to the cold. However, more investigation is needed on that point.