All serious butterfly collectors remember their first gynandromorph: a butterfly with a colour and pattern that are distinctly male on one wing and female on the other.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/how-split-sex-insects-and-birds-are-helping-science
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/hindu-new-delhi
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/environmental-science
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/birds
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/insects
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/butterflies
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/united-states-america-us