Do I understand you correctly that you did the Trader Joe challenge and hatched out commercial eggs you got from a Trader Joe's grocery store?
Good for you! That is a challenge as they've been refrigerated and transported numerous times.
It won't be any breed then as it would be likely a hybrid of Production Red and something else...possibly between Production Reds or between Red Sex Links or whatever the farm has free ranging. I can tell you that no Barred Rock was used as the rooster (no barring), and no White Leghorn was in the production (not dominate white).
What color was the egg? That will give you some clue. (If I remember correctly, the fertile Trader Joe eggs were usually brown).
As to gender...some of the comb looks a bit larger for 4 weeks, another couple of weeks will let you know.
Hybrid pullets tend to mature quickly, so as long as the comb stays yellow, even if it gets some taller "teeth" to it, it usually will be a pullet.
Re-post in a couple of weeks...and I'd love to hear the details if you truly mean the Trader Joe's challenge....how many did you set...is this the only one that hatched?
LofMc