  New criteria are shown that certain combinations of finite unimodal
polynomials are unimodal. %Given unimodal polynomials with explicit expressions
and dependent recursion relations, we propose an approach to determine their
modes. As applications, unimodality of several polynomial sequences satisfying
dependent recurrence relations and their modes are provided. Then unimodality
of genus distributions for some ladders and crosses can be determined. As
special cases, that of genus distributions for Closed-end ladders, circular
ladders, M\"{o}bius ladders and Ringel ladders and their modes are given, which
induces the known results for Closed-end ladders.
