Yay! Science Stuff
There are chickens that are half female and half male—literally. We’re not talking about hermaphrodite chickens, we’re talking about left-half-male and right-half-female chickens.
A team of research scientists at the University of Edinburgh procured three of these fantastical gynandromorph creatures and published their study in 11 March edition of Nature, after they found that development of sex determination is different for birds.
The traditional view was that birds were the same as mammals, in that a sex-determining gene triggers male or female sex organ development, which in turn determines male or female hormonal secretions. One of the effects of those secreted hormones is that the male or female body-type develops. However, by studying these half-rooster-half-hens the researchers found that in fact each cell of the chicken has its own sex identity determined by its genes.
Using molecular biology techniques, the researchers determined that roughly half of the cells in each bird had the male genotype (ZZ in birds) and the other half the female genotype (ZW). Neither side was completely male or female, but the side that looked male had more male cells and the side that looked female had more female cells. Furthermore, by implanting pieces of male or female sex organs in their respective opposites, the researchers determined that the environment of the sex organ did not affect the development of the tissue; pieces of testes continued to develop as testes and pieces of ovary as ovary. This experiment strongly supported the researchers’ idea that each cell possessed an individual sex identity.
Perhaps the coolest question raised by these gynandromorph chickens is ‘how?’, and this study shed light on even that question. While it was initially believed that gynandromorph birds arise from a mutation at an early stage of development, this study supports the idea that these dual-sexed birds are the result of the fertilisation of a dual-sexed egg.