Why aren't there equal numbers of boys and girls born?


We’ve all heard of the instances where the gender ratios alter naturally to compensate for loss. For instance, after the World Wars, more boys were born. Or in nature, many mammal species with adjust the ratio of male to female when its herd numbers are threatened. The process has been identified but never explained. A new study from the University of Veterinary Medicine in Vienna may have figured out how the survival of female embryos may be enhanced under conditions that would otherwise tend to favor the birth of males.

Symmetry in sexes is often skewed

There is a symmetry in the system of reproduction which should ensure roughly equal number of males and females. However, this is often not the case. Researcher Jana Beckelmann has presented evidence that a particular protein, insulin-like growth factor-1 or IGF1 might be responsible. By looking at 30 embryos, Beckelmann found that during early pregnancy the level of messenger RNA encoding IGF1 protein was present in embryos revealing that the messenger RNA is translated to protein.

IGF1 for cell health and protection

IGF1 is already known to inhibit programmed cell death. Once implanted into cattle, the protein improves their survival. And it has positive effect in the early embryo of the horse. But why do females have more of the factor than males? It may be that the female embryos need it to survive.

IGF1 boosts survival of embryos, may help females

Horses experience an unusually high number of losses in early pregnancy, most of them female. The male embryos are better equipped to handle the high levels of glucose found in well-nourished mares. This then gives a preferential ratio to male births. Beckelmann explained, “We think the higher IGF1 concentrations in female embryos might represent a mechanism to ensure the survival of the embryos under conditions that would otherwise strongly favor males.” The selective nature of the presence of IGF1 indicates an interplay between environmental and internal factors.

Source: MedicalNewsToday, University of Veterinary Medicine


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