A rare condition in which people’s internal organs grow on the wrong side of the body could be better understood - thanks to snail shells.
Researchers have pinpointed a gene in snails that determines whether their shells grow clockwise or anticlockwise.
Their finding could offer clues as to how the same gene affects body asymmetry in other living things, including people.
While most animals and people appear symmetrical on the outside, almost all have an asymmetrical arrangement of internal organs.
About one in 10,000 people are born with their major organs on the wrong sides of their bodies.
The condition, Situs inversus, generally has no symptoms but has been a longstanding genetic puzzle for scientists.
A combination of traditional science and new tools has enabled stunning insights into early development.
A team of scientists led by the University of Nottingham and Edinburgh, in collaboration with the University of Göttingen and Tufts University in the US, identified a gene in snails that controls whether their shells twist clockwise - which most do - or anticlockwise.
Scientists pinpointed the location of the gene on the snail’s DNA, then used genome sequencing technologies to identify the single flaw that causes anticlockwise shell development.
The gene makes a protein called formin - a building block of the structures that give cells their shape.
The gene defect results in absence of formin in early embryo development, causing snails to have mirror image bodies and anticlockwise shells.
Studies in frogs showed the gene has a similar function in the early development of creatures with spines - including people.
The results suggests that all animals with a symmetrical appearance have developed similarly, from early embryo formation, throughout evolution.
The research, funded by the Biotechnology and Biological Sciences Research Council, was published in Current Biology.
We were able to use cutting-edge DNA and computer analyses to decode snail genes, then identify the one letter changed in a billion that causes shells to grow anticlockwise.