Crime and twins

Crime and twins

Twins' DNA hinders France sexual assault investigation

Police who are investigating a series of sexual assaults in the southern French city of Marseille have arrested identical twin brothers.

The 24-year-old unemployed delivery drivers, named locally as Elwin and Yohan, were placed under investigation on Friday.

Officers say they are sure that one of the two men carried out the attacks, but that they do not know which.

Standard DNA tests are unable to differentiate between their DNA.

...

Police have been told it would cost upwards of 1m euros (£850,000) to conduct an ultra-sophisticated genetic test that would be able to tell one set of the twins' DNA from the other.


One expert told the French newspaper La Provence: "For a normal analysis, we would compare 400 base pairs [of nucleotides] which make up DNA."

In the case of identical twins, he added, "We would be looking at billions."

I wonder what is the ultra-sophisticated genetic test they are referring to; presumably no genetic test can be any more sophisticated than a whole genome sequence at very high coverage, and that does not cost a million euros anymore.

The closest I could find on the topic of twin genetic similarity is the following reporting on an ASHG 2012 abstract:

They then calculated the frequency with which these mutations occurred. Only two sets of twins had such mutations, which translates to a DNA change occurring once for every 10 million to 10 billion bases that are copied every time a cell divides. While that may seem like a high accuracy rate, cells in the body divide trillions of times. So that would mean an average twin pair carries 359 genetic differences that occurred early in development. 

One limitation of the study is that they could only estimate the mutation rate based on blood cells, but some cells in the body divide much more frequently and so may rack up many more mutations. Other cells, like brain cells, don't regenerate much and would probably remain stable.

Beware of who you kiss

Beware of who you kiss

Forensic Sci Int Genet. 2013 Jan;7(1):124-8. doi: 10.1016/j.fsigen.2012.07.007. Epub 2012 Aug 20.

Prevalence and persistence of male DNA identified in mixed saliva samples after intense kissing.

Kamodyová N, Durdiaková J, Celec P, Sedláčková T, Repiská G, Sviežená B, Minárik G.

Abstract

Identification of foreign biological material by genetic profiling is widely used in forensic DNA testing in different cases of sexual violence, sexual abuse or sexual harassment. In all these kinds of sexual assaults, the perpetrator could constrain the victim to kissing. The value of the victim's saliva taken after such an assault has not been investigated in the past with currently widely used molecular methods of extremely high sensitivity (e.g. qPCR) and specificity (e.g. multiplex Y-STR PCR). In our study, 12 voluntary pairs were tested at various intervals after intense kissing and saliva samples were taken from the women to assess the presence of male DNA. Sensitivity-focused assays based on the SRY (single-copy gene) and DYS (multi-copy gene) sequence motifs confirmed the presence of male DNA in female saliva after 10 and even 60min after kissing, respectively. For specificity, standard multiplex Y-STR PCR profiling was performed and male DNA was found in female saliva samples, as the entire Y-STR profile, even after 30min in one sample. Our study confirms that foreign DNA tends to persist for a restricted period of time in the victim's mouth, can be isolated from saliva after prompt collection and can be used as a valuable source of evidence.

Link

Upcoming Richard III documentary

Upcoming Richard III documentary

From Channel 4:

With the support of historians, the University of Leicester's archaeologists identified a possible location of the monastery as the car park for Leicester City Council's Social Services department. However as Richard Buckley, Head of the University of Leicester's Archaeology Services tells the programme: "...the chance of finding Richard was, I don't know, a million to one." Yet the dig commenced and on the very first day a male skeleton was discovered - which careful examination would later reveal to have curvature of the spine and battle injuries including a head wound.

For the last three months, the remains has been subjected to some of the most cutting edge technology and forensic testing in existence - with Channel 4 capturing every moment. In specialist labs in Leicester and across the country, the bones have been subjected to CT scans, they have been carbon-dated, DNA has been extracted to be compared to that of one his living descendants, the source of the spinal curvature has been investigated - and the entire body has been subjected to rigorous testing to reveal blow-by-blow how this individual died and how he was buried.

Perhaps most fascinating of all, using technology developed to identify human remains in crime investigations, scientists have been busily re-creating the face these bones belong to - this image will be revealed exclusively in the programme the night it airs. And of course, Richard III: The King in the Car Park will reveal the results of what could be one of the most astonishing archaeological discoveries in recent history - whether England's missing king has indeed been recovered.

This will air on Feb 4.