Sex mosaics

This is a sex mosaic ('mosaic gynandromorph') Papilio dardanus from our breeding experiments last summer. The left wing is mostly the pattern of the female form cenea, but the right wing shows lots of yellow patches of male pigment. There is even a segment at the bottom corner with male patterning and even a little bit of a tail.

It is thought that this kind of pattern arises (in Lepidoptera at least) from the loss of one of the female-specific sex chromosome from one of the two daughters of a cell division. In butterflies and moths, the sex determination system is the other way around to humans - males have two identical sex chromosomes (ZZ rather than XY) and it is the females with two different sex chromosomes (ZW contrasting with XX in humans). If this loss happens very early in development whilst the embryo is only a few cells, the result can be a striking bilateral gynandromorph:

[Papilio dardanus bilateral gynandromorph - left side female form cenea, right hand male]

However, if the error occurs later in development, the result will be a mosaic as in the first picture. Isn't biology cool?!