function mainplot(trait, marker, mnames)
%make an main effects plot
K = max(marker)+1;	%2 for BC, 3 for F2
means = zeros(1,K);
ns = zeros(1,K)
stds = zeros(1,K);
for i = 1:K
   means(i) = nanmean(trait(find(marker==i-1)));
   ns(i) = sum(~isnan(trait(find(marker==i-1))));
   stds(i) = nanstd(trait(find(marker==i-1)));
end
stds = stds./sqrt(ns);
plot(means,'-d')
axis([0.5 K+0.5 .9*min(min(means-stds)), 1.1*max(max(means+stds))])
hold on
for i = 1:K
   plot([i,i]',[means(i)-stds(i),means(i)+stds(i)]','+:')
end
set(gca,'XTick',[1:K])
if K == 2
   set(gca,'XTickLabel',['AA';'AB'])
else
   set(gca,'XTickLabel',['AA';'AB';'BB'])
end
if nargin>2
   xlabel(mnames(1))
end
hold off