Monozygotic Twins

How can scientist tell identical twins apart if they were both suspects in a crime? With new technology now that is possible.

Background: Monozygotic twins are considered genetically identical; therefore they cannot be differentiated when using standard forensic DNA testing (Weber-Lehmann, et al, 2014). Bioinformatics analysis in the past has found single nucleotide polymorphisms (SNPs) present between identical twins. This gives evidence for the hypothesis that rare mutations will occur early after the human blastocyst has split into two. (Weber-Lehmann, et al, 2014) Paternal testing usually looks for short tandem repeat markers, but monozygotic identical twins have the same microsatellite profiles. About 80% of one twin usually carries

(Weber-Lehmann, et al, 2014). Mutations in the somatic cells will not be transmitted to any potential offspring. (Weber-Lehmann, et al, 2014). These de novo mutations will help determine the twins a part. The mutations occurred after separation between the twins. Mutations that are present in one twin’s sperm and buccal mucosa and not in blood will have occurred after gastrulation (Weber-Lehmann, et al, 2014). A mutation present in all three tested tissues must have occurred earlier before the separation of germ layers (Weber-Lehmann, et al, 2014). The mutations only present in the sperm occurred the latest after the split in the twins. Most mutations observed are in the buccal mucosa and sperm that suggest the buccal mucosa is the starting material to determine mutations between monozygotic twins (Weber-Lehmann, et al, 2014). A sampling of buccal mucosa is legally and ethically easier than sampling sperm. New technology is showing scientist that twins are not 100 percent the same and it is possible to tell them a part. With this new technology, it is possible to tell which twin actually committed a crime and

Another way to sequence the genome is to use the parent’s children as a baseline. They would take the mother’s DNA and compare it with the child to see what DNA was inherited from the father. Then compare the child’s DNA to the uncle and see if there are SNPS that the child has but not the uncle. Those are the different SNPS regions where the twins are different. SNPS will then be confirmed by classical Sanger sequencing. Methods provide a solution to solve paternity and forensic cases monozygotic twins as alleged fathers or committers of a crime. To avoid bias the lab team would not be informed of which twin is the real father. The twin’s blood, sperm, and buccal mucosa will be sequenced to look for SNPs in somatic and germ line cells. The sequences will be performed on a Illuminia HiSeq 2000. The mutations will be separated by chromosome. Primers will be used to amplify upstream and downstream of the regions of interest. The possibility that the mother inherited the SNPs to the child will be excluded. By testing the sperm, buccal mucosa, and blood it will overcome problems that will show mosaic de novo mutations where the mutation is only in one form of the tissues. The references samples for the monozygotic twins will be analyzed in all next generation sequencing