Researchers at Stanford University have just sequenced a child’s DNA from a sample of mother’s blood. This instance of non-invasive DNA testing is a major breakthrough because it doesn’t need either fetal samples or paternal DNA. Current fetal testing involves amniocentesis, which uses the amniotic fluid by injecting a needle into the womb, which carries a minor risk of complications.

Floating DNA in Mother’s Plasma
A portion of the floating DNA in a pregnant woman’s plasma (which is the liquid in which blood cells float) is that of the foetus. This DNA is first extracted and then ‘shot’ into millions of small fragments (this method of sequencing genomes is called ‘shotgun sequencing’), following which they are sequenced, analysed and re-assembled into one complete genome. If you’re wondering why they are broken down in the first place, it’s because we don’t have the  technology that can sequence the entire genome (which is 3 billion letters long) at one go.

This is actually a representation of DNA fragments from many more than two genomes (this is from a marine microbial community), but it gives you an idea of the magnitude of assembling millions of tiny sequences into two gigantic ones.

Untangling Two Genomes
What has been difficult is the separation of these fragments into two complete genomes- the mother’s and the foetus’s. Scientists have now come up with algorithms that are smart enough to detect this, one step ahead of previous research which used mother’s blood but also needed the father’s DNA for sequence mapping. “It is not that practical to assume you can get DNA from dad or you even know who dad is,” said Stephen R. Quake, a professor of applied physics and bioengineering at Stanford and senior author of the study.

Progress in this technique could help us move forward in fetal disease screening and prevention, when it may be possible.