In a one-trait test cross, the phenotype that disappears in the f1 generation is the a. dominant trait b. negative trait. c. recessive trait d. heterozygote

The answer would be c. recessive trait.

If you imagine a cross involving height: TT for tall, tt for drawf:

The P generation (test cross) means you're crossing a homozygous recessive with a dominant. A TTxtt cross would produce four Tt offspring, all tall (the dominant trait).

fumikage isn't really a bird, and tsuyu does have teeth. tsuyu has a transformation quirk which still allows her to be partially human. otherwise we'd have a large frog running around. fumikage has teeth because again, he isn't a bird. his head was a quirk mixture if i'm correct.