What are some examples of biotic factors that affect carrying capacity?

Factors like native plants and other animals competing for the resources.

Explanation:

The most important one for human civilization would definitely be the native plants because they will turn to be the ones that can be cultivated in that specific type of soil. For example, in the raining forests, cultivation like potatoes is not possible, because it's not a native plant. Another factor could be the other animals, or native animals, that compete for resources in that ecosystem, as they also interact with it, they would also be part of the decrease or increase of carrying capacity.

multiple allele inheritance is traits controlled by more than 2 alleles (ex: pigeons having 3 alleles of one gene govern their feather color).   so the answer is a.