Question

What combination of alleles could produce a trait controlled by a recessive allele?

Answer 1

I don't know. But alleles is one or more alternative form of a gene, and recessive allele is two genetic genes that the offspring inherited from both parents.

Answer 2

so you have dominant alleles that are represented by capitals and recessive represented by lowercase, we'll just use B and b in this example. Genes are expressed from combination of 2 alleles that are either BB, Bb, or bb, when there's at least 1 dominant (capital) then the dominant trait is expressed, and only if there are 2 recessive is the recessive trait expressed.
so it would only be 2 recessive alleles.