Additional Sunday post

I do not usually post twice in one day, but this is far too cool to not post about:

There is a phenomena in nature known as gynandromorphy, which means that an organism displays both male and female characteristics.  This is different from hermaphroditism, which only refers to the sexual organs.

This appears to be mostly within insects, but some crustaceans have been found to have it too…This post is not about those, but these pictures of butterflies illustrate what it means (image from wikipedia):


That is interesting, I can hear you saying, but is it worth another post on a Sunday?

Well….you might not think that butterflies are cool enough for that, but, I think this is extra awesome:

Gynandromorphy in chickens. Image from

The REALLY cool thing about this is not just that it is a half male, half female chicken, but what this tells us about how chickens sexual characteristics are determined.

In humans, our male, or female characteristics are determined by our hormones when we hit puberty. There are variations within each sex, with some men being extremely hairy, others who are almost hairless, likewise with women, as well as our overall body shape.

In chickens (and possibly other birds) the sexual characteristics of the animal appears to be determined primarily by the chromosomes, instead of by hormones (so in humans, it would be XX or XY, there are variations on this, but that is a whole other post).

This image illustrates the differences between how chickens and humans develop sexual characteristics (Full link to article in references)

Differences in how mammals and chickens determine sexual characteristics. Image from Not Exactly Rocket Science

Bilateral Gynandromorphy is usually seen in insects, and is down to the way that their cells are determined during development, and I will try to explain. This is a bit complicated, but it is due to at which stage of division after fertilisation the gynandromorphy occurs.  Early on in development, between 8 and 64 cells into division (see references for info) if a chromosome (X or Y in humans) is left behind in the nucleus after division, this leads to a 50/50 bilateral gynandromorphy This is because early cell division determines the left and right sides of an organism.

Mosaic gynandromorphy occurs when a chromosome is left behind more than once during the developmental process.

The strange thing with birds appears to be that even though the gynandromorph chickens have a mix of chromosomes (Z or W in chickens) throughout their body (This was tested by tagging the chromosomes with a fluorescent molecule), one side had more female cells and one had more male cells.

Further testing showed another anomaly between birds and mammals.  In mammals, if you put an XY cell (male) into an XX environment (say, an ovary), the male cell will become a functioning part of that region, and act like the other cells around it in response to sex hormones, however, when this occurs in a bird, the cells continue their original sex designation.  So, when researchers put a lot of ZW (Female) cells into a ZZ environment, and subjected them to the hormones, the cells continued to produce female enzymes, and female structures.

As that was quite technical, I will end with some cool pictures of this, including one where the difference is not immediately obvious (all images from Dalton State College):

Butterfly bilateral gynandromorph

Bilateral Gynandromorph, slightly female on left back wing (the grey)

Moth (Malacosoma disstria) bilateral gynandromorph. The female half is the left side.


References/Further Reading










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