documentclass[a4paper,12pt]{article}
usepackage[all]{xy}
usepackage{amssymb}

begin{document}
xymatrix@R=1.4pc@C=1pc{
K_0(M_poplus M_q)oplus K_0(C([0,1]),M_poplus M_q))ar@{-}[r]&\
K_0(Z_{pq})  ar[u]^{K_0(pi_1)oplus K_0(pi_2) } \
ar[u]}
end{document}

documentclass[a4paper,12pt]{article}
usepackage[cmtip,all]{xy}
usepackage{amssymb}
begin{document}
xymatrix@R=1.4pc@C=1pc{
K_0(M_poplus M_q)oplus K_0(C([0,1]),M_poplus M_q))ar@{-}[r]&\
K_0(Z_{pq})  ar[u]^{K_0(pi_1)oplus K_0(pi_2) } \
ar[u]}
end{document}