Mendel examined seven characteristics in his pea plants. He crossed two plants with different forms of a trait (like tall plants and short plants). In every case, the first generation of plants (F1) were .

dominant

Explanation:

For every trait, there are two types of characters - dominant and recessive which are determined by the combination of the alleles for a given gene.Each gene has 2 types of alleles- one is the dominant allele which always expresses itself that is in both homozygous and heterozygous conditions whereas the other one is the recessive allele which can only express itself in the homozygous conditions. In Mendel's experiments when he crossed plants with different traits he observed that in the F1 generation there was always a single trait that was getting expressed and it was the trait that was being coded by the dominant allele.