Genes control the way an embryo develops
The breakthrough provides valuable information about the way genes are regulated in the developing embryo.
It should also help improve the understanding of foetal loss, tumour development, birth defects and mental retardation.
The scientists, from the University of North Carolina at Chapel Hill, carried out their research on female mice embryos.
They examined a gene called eed, which when functioning normally keeps the X chromosome inherited from the father inactive, and many of its genes shut down in early placental cells.
They discovered that female embryos without a functioning eed do not survive because they cannot form a placenta.
Molecular brakes
Other studies have shown that the gene Xist is responsible for putting the molecular brakes only on the X chromosome.
As female mammals have two X chromosomes (XX) and males an X and Y (XY), imbalance occurs because female embryos have twice as many X-linked genes.
That is where Xist comes into play. It gets turned on early in the development of the female embryo.
This gene is activated from the X chromosome that is going to be shut down - which in early placental material is only the X from the father.
Once the paternal X chromosome is shut down, then the cells must continue to divide and keep it shut down.
The new research has found that it is the eed gene which performs this function.
Switches on
Lead researcher Dr Terry Magnuson said: "Without eed functioning normally, the father's X chromosome is shut down and then it comes back on.
"When that happens, too many X chromosome genes are active, there are problems forming placental tissue, and female embryos die."
The researchers also discovered that a partially-functioning eed gene can lead to the development of leukaemia, skeletal abnormalities and other problems.
The gene also plays a vital role in telling cells where to go in the developing embryo.
Without this gene functioning in the proper way, those cells move to the wrong place. And that can result in birth defects.
Dr Magnuson said: "We've learned from the human genome projects that there are far fewer genes than were originally estimated, roughly 35,000.
"In a complex organism like humans, those 35,000 genes must act in concert with one another in many different combinations at many different times.
"So understanding how genes are regulated in terms of their expression, how they are turned on and off, and if they are off how they are maintained in that 'off' state, becomes critical in the post-genome era of understanding gene function."
The research is published in the journal Nature Genetics.