When women sacrifice eggs to make healthier babies

Women sacrifice a lot for their families and for the sake of giving birth to healthier babies, they do not even spare their own eggs, a study has said.

The most stringent egg selection takes place at the earliest stages.

"Our findings suggest that the ovary of a newborn girl already contains both 'good' eggs and those destined to give rise to down syndrome or miscarriages," said Alex Bortvin from Carnegie Institution for Science in the US.

Even before a baby girl is born, she has already lost 80 percent of her initial pool of immature eggs during fetal development.

The fetal egg die-off is connected to segments of the egg's DNA known as transposable elements or jumping genes, the researchers discovered.

As developing eggs gain the ability to guide embryo development, transposons gain the ability to start moving.

These ancient virus-like genes begin to leapfrog around the egg's DNA, thereby producing new mutations.

The researchers discovered that female mice allow transposon movement to take place, but then get rid of immature eggs harbouring the highest number of mutations before the female mouse is even born.

This purging process allows for the selective survival of immature eggs whose genetic material has acquired relatively few new mutations, the researchers proposed.

Despite their destructive power, jumping genes are also the source of serendipitous genetic novelty that can make species stronger and better suited for survival over time.

By allowing just the right amount of beneficial transposon-generated genetic variation, female mammals give their offspring and species the best chance of thriving in an uncertain, dangerous world.

The study appeared in the journal Developmental Cell.