Purchased from feed store on 3/11, though probably had been in the brooder there for a while, so no idea what age. The other Ancona chick I purchased that day has no comb at all yet. Do I have a roo here?
I agree rooster...that much red comb on a chick that is clearly 6 weeks or younger...rooster. (Estimated age from your statement that you picked up 3/11 so 2 1/2 weeks ago...it wasn't a fledged mature chick yet...so had to be under 4 weeks at time of purchase???...puts this chick in the 4 to 6 weeks now at most.
Good news is most feed stores take roosters back...and you could swap for another bird if you desired...just choose one similar in size/age if you can that matches the female Ancona.