Glaucoma is a leading cause of blindness. studies have linked a common form of glaucoma to three genes and more than 20 genetic loci. which best describes glaucoma? a. a recessive trait that requires multiple recessive alleles to be expressed b. a polygenic trait that is influenced by the number of alleles present c. a codominant trait that is expressed more often when more dominant alleles are present d. a dominant trait that depends on the presence of only one of many dominant allele