My girls are hatchery stock and most have buds, my Polish though has full blown spurs. It can happen as a result of line-breeding, inbreeding, etc...
I always feel better knowing my girls have some protection with them.
This is, however, an acquired gene. My Polish hen was bred to my Sultan roo and the offspring, a pullet, is less than a year old, already having the start of spurs on her legs.