If we look at what Mendel learned from studying pea plants we can also see how this affects certain characteristics in chickens, such as pea-combs are dominant over single-combs. A pea-comb cock crossed with a single-combed hen will result in pea-combed offspring, but only in the first generation. But if breeding is continued, such as in the case of inbreeding or line-breeding, using the pea-comb offspring, bred back to their parents, this would give you, in the second generation, a mixture of pea-comb and single-combed offspring. Although the resulting offspring all came pea-combed, they now also carry the recessive trait for single-comb.