“Identical” twins
Now there’s a study that shows that identical (monozygotic) twins do not have identical genomes (I spotted it here at DNA Direct talk — I’m getting a lot of science news now that I follow the DNA network).
The genomes are pretty close, but not identical. There seem to be a lot of structural variation between them.
I guess it doesn’t surprise me all that much, even if it looks like a major discovery. Considering that the cells within an individual have almost but not quite identical genomes, I would be very surprised if twins’ genomes were identical.
For reading about the somatic cell differences, this is an excellent paper:
Genomic Variability within an Organism Exposes Its Cell Lineage Tree
Frumkin D, Wasserstrom A, Kaplan S, Feige U, Shapiro E
Genomic Variability within an Organism Exposes Its Cell Lineage Tree. PLoS Comput Biol 1(5): e50 doi:10.1371/journal.pcbi.0010050
What is the lineage relation among the cells of an organism? The answer is sought by developmental biology, immunology, stem cell research, brain research, and cancer research, yet complete cell lineage trees have been reconstructed only for simple organisms such as Caenorhabditis elegans. We discovered that somatic mutations accumulated during normal development of a higher organism implicitly encode its entire cell lineage tree with very high precision. Our mathematical analysis of known mutation rates in microsatellites (MSs) shows that the entire cell lineage tree of a human embryo, or a mouse, in which no cell is a descendent of more than 40 divisions, can be reconstructed from information on somatic MS mutations alone with no errors, with probability greater than 99.95%. Analyzing all ~1.5 million MSs of each cell of an organism may not be practical at present, but we also show that in a genetically unstable organism, analyzing only a few hundred MSs may suffice to reconstruct portions of its cell lineage tree. We demonstrate the utility of the approach by reconstructing cell lineage trees from DNA samples of a human cell line displaying MS instability. Our discovery and its associated procedure, which we have automated, may point the way to a future “Human Cell Lineage Project” that would aim to resolve fundamental open questions in biology and medicine by reconstructing ever larger portions of the human cell lineage tree.
The applications for analysing genetic diseases that the researchers mention still makes this an interesting result, if only you can find sufficent twins with one affected and one unaffected twin…