No one can force you to do anything at school, they can tell you to do something, but they can't force you.
I guess it's up to you if you want to get the grade or not disect.
That's a bit harsh, without the grade he could potentially miss out on a high op and get into vet school or something similar which would help a lot of animals.
You should be able to just group with someone if it comes down to it, and not actually do any of the dissecting, they usually don't use full animals, but it's a possibility.
Maybe have a word with your biol teacher, they usually have a set out curriculum they adhere to, so they should be able to tell you if there's any dissecting, and if there is, get onto the teacher early and explain the situation, you should be able to work something out! They're usually pretty accomodating as long as you want to learn, and are doing good.
(hint: I did biol and genetics in grade 12, and I never had to do a dissection

)