Eric and janelle are both carriers of the recessive allele causing tay-sachs disease, which is lethal in early childhood. if they have a baby, what is the probability that this child would have tay-sachs disease?

25% would have tay-sachs disease, 25% normal, 50% carriers

A dichotomous key works by giving you a list of options that must be fulfilled for you to call an animal a certain species. It is like a list of traits that help you differentiate between species. The major factor is that there are no things on the key that will help her differentiate, meaning that it's a new species because its traits are not there.