Dimorfismo sexual y desviación en la proporción de los sexos en embriones preimplantatorios

sexual differences in size and morphology are common in the animal kingdom and they have been mainly explained by sexual selection. according to classic theory of sexual determination and differentiation, the morphologic differences between the same specie individuals both different sex starts to show up soon after and as a consequence of the gonads formation and development. however, increasing evidence coincide in signaling that differences between males and females star to be evident long before of gonads formation, from preimplantatory stadium (week 1) or even from zygotic stadium (day 1). differences in kinetics of development and in energetic preimplantatory metabolism have been explained by genetic and epigenetic differences which underlie it and, in the case of get persistent, they can take them until disrupting the normal sex ratio. in this review about sexual dimorphism in preimplantatory embryos hypothesis, accumulated evidences and scenarios (in vivo e in vitro) are explored, as well as the last findings and possible changes that will have to be faced by the embryology.