This diagram shows how seed plants are grouped.

A diagram shows how seed plants are grouped. Seed is split into gymnosperms and a question mark.

Which is the missing label?

Choose the best definition of allele. a. one of several possible versions of a gene, which each produce a different phenotype b. an organism that's purebred for a given trait c. the process of fertilizing a plant with pollen from another plant d. a set of genes that are located on the same chromosome and so are tightly linked