I found this today and I'm finding it pretty interesting! lets see if I can explain this simply and correctly: in birds, the female controls the offspring's gender (ZW)instead of the male in humans (XY) the female basically has all the necessary information to be male(Z), but is is overridden by the female genes (W) The hen, like most other animals, has two ovaries, but only one functions, the left. The left contains all egg cells and hormones (basically the information on the female chromosome, W). the other serves no real purpose, and does not contain these hormones. if something happens to the left, functioning ovary (usually disease) the right ovary is then stimulated to grow rapidly to produce the body's hormones. but it cannot produce estrogen so it produces testosterone. this causes the "Hen" to now become a rooster for most intents and purposes. this can include, while rarely, the formation sperm.The hen can then "father" Offspring! How weird is that!? the resulting offspring are 1/2 of the chicks female, and 1/4 male. 1/4 not ever developing. http://edis.ifas.ufl.edu/PS050 I can't find any practical use for doing this one thought I did have is that if the hen produces egg cells and you freeze them; you could then fertilize "Her" own eggs by "Himself" One example I found of sex reversal in chickens is Freaky the Wyandotte, in the UK. In this case, she laid numerous eggs until one day she got hackle and saddle feathers, began to crow, etc. in this case it was not fertile. I'd like to add that NO ONE should try doing this! this is a miracle of nature, and I'm merely curious and find it very interesting.