Mendel was able to study seven traits in all the pea plants in each generation. which of his hypotheses allowed him to analyze each trait separately? if two different alleles for a gene occur together, one of the alleles may be expressed while the other is hidden. when gametes are formed, each gamete carries only one allele for the gene. there are alternate versions of a alleles called genes. for each inherited trait, there is only one copy of the gene that codes for that trait.