Jacqueline Weber-Lehmann, et al., Finding the needle in the haystack: Differentiating “identical” twins in paternity testing and forensics by ultra-deep next generation sequencing, FSI Genetics, 2013
We sequenced DNA from sperm samples of two twins and from a blood sample of the child of one twin. Bioinformatics analysis revealed five single nucleotide polymorphisms (SNPs) present in the twin father and the child, but not in the twin uncle. Our results give experimental evidence for the hypothesis that rare mutations will occur early after the human blastocyst has split into two, the origin of twins, and that such mutations will be carried on into somatic tissue and the germline.
Potential somatic mutations were screened and compared to the mapping results of the child.
Interestingly, four of the five mutations seen in the sperm DNA of the twin father are also present in his buccal mucosa DNA. Only one of those four mutations is also seen in the blood DNA.
Generally, without involving identical twins, the estimated number of SNP substitution rates per generation ranges from 1 to 3 x 10-8 per human single base-pair, equal to approximately 10-40 expected SNPs per paternal generation.
In addition, similar findings confirm the common phylogenetic history of buccal mucosa and sperm cells, both belong to the ectoderm germ layer and help to narrow down the history of the somatic mutation event: mutations that are present in one twins’ sperm and buccal mucosa, but not in blood, will have occurred after gastrulation, but before the separation of the buccal mucosa and the precursors of the sperms.
The fact that most of the mutations we identified are present in the two ectodermal tissues, buccal mucosa and sperm, suggests the use of buccal mucosa as starting material for identification of mutations between MZ twins.
Genome is different even in monozygotic twins.