Although in the classic scientific literature the sex determination is attributed to the presence of the X and Y chromosomes during last years a new information has been surged, stage by stage, they led us to mammals, birds, reptiles , fish up to similar phenomena in plants.

It is known that in mammals the presence of XX determines female gender and the presence of XY determines male gender. However the observation of avian genome shows that an individual XX is a cock and XY genome is a hen. In other vertebrates may be presented male individuals with XO, XXY and female with XXX.

The discovery of the SRY gene in mammals, allegedly originated from duplication occurred about 160 million years ago, the SOX3 gene linked with the X chromosome could explain that these genetic manifestations are not exclusively related to the chromosomes. Other phenomena such as temperature and social events can influence on the determination including changing sex of an individual without existing a genetic change.

So in reptiles and fish sex determination is influenced by ambient temperature during incubation, as in the case of some reptiles such as crocodiles and fish (CYP19 gene) and is also known in some fish (guppies Poecilia reticulata) the absence of any male individuals causes of female sex change, becoming a functional male, thereby allowing the production of a new generation with individuals of both genders.

These phenomena relatied to the determination and sex-change seemed an animal phenomenon so far, but recent studies in the tree Taxus baccata indicate that the phenomenon could have a plant origin and therefore be older than 160 million years known until the now.

Taxus baccata is a dioecious tree (there is separation of sex between individuals), like other primitive plants as Ginkgo bilova, but has recently been discovered that a male T. baccata can cause female branches. Given the slow phase of life of high plants are still unaware of the causes of such phenomena.

However this information opens a connection between the animal and plant genetics. In the production of oxygen, carbohydrates and acid the animal and plant mechanism circulate in opposite direction. So the oldest higher plants are dioecious while the modern tend to be monoecious (individuals with both sexes), while the oldest animals are monoecious and the modern tend to be dioecious.

Photo by Jared Belson