BUILD A SNOWMAN: As we move down the puzzle, a SNOWMAN - an abominable SNOWMAN, that is - is being built at the front of the theme answers. We start with Y, then YE, then YET, then YETI.

BUILD A word themes are fun, and this is no exception. When I filled in Y CHROMOSOME, the single Y at the beginning clued me in that we would be building a word. I admit that I didn't catch on that we were building the word YETI until much later, making for a nice "Aha!" moment. I kept thinking of Olaf, the SNOWMAN from Frozen, even though there's no Y in his name. Thank you, Zhouqin, for this delightful puzzle.