Student or Learner
Caribou are the only deer in which males and females both have antlers -- though only some females have them.
Is 'in which' correctly used? I would use 'whose' instead.
I'd also add "the only species", but I think this allows "in which".
ie. Caribou are the only species of deer in which males and females both have antlers."
Or you could write, "The only kind/type of deer"
"In this species/type/kind of deer both males a females have antlers" is better than "In these deer, both males and females have antlers".
I agree with Tan Elaine.
I see no reason to go out of your way to avoid whose.