Getting the picture from DNA.

  At present, if police find DNA which could be that of the criminal at the scene of a crime (for example in blood or hair), standard forensic techniques can help in two ways. If there’s a suspect in custody, the police can see if their DNA matches the ‘crime stain’, as it is called. In the absence of a suspect, they can see if it matches the DNA of any known criminal held in their archives.

  Both techniques have proved their worth in criminal investigations. But what if there’s no suspect and no match in the archive? Ever since DNA testing was introduced, forensic scientists have wondered how much a DNA sample on its own could tell them about what a criminal might look like.

  Scientists have already had some success with predicting hair colour from DNA samples. For example, researchers at Britain’s Forensic Science Service (FSS) have developed a DNA test which will tell with 98% accuracy whether or not someone has red hair. However, the red-hair test is of limited use in Britain, where only 6% of the population are red-haired. What about blonde, brown and black-haired criminals? Hair colour is usually determined by the cumulative effect of several genes, so unfortunately there’s no such thing as a single gene for blonde hair that could be turned into a simple test, for example. It’s the same with eye colour.

  But biotechnology firm DNAPrint Genomics of Florida, USA, is having a crack at both problems. As a starting point, research was carried out using mice to discover the genes that controlled eye colour. Similar sequences in human DNA were then investigated, and ten possible genes were found. Next, the DNAPrint researchers took DNA samples from 500 volunteers and recorded their eye colours. They then applied a technique called SNP mapping to see if they could discover any correlations between the two. (SNP stands for “single nucleotide polymorphism” – a single ‘letter’ change in the genetic code. These variations account for most of the genetic differences between individuals.) The researchers sequenced the ten possible genes from each volunteer, then sifted through the sequences looking for SNPs. They found 50 in total. Thn they set computers to work out how the SNPs correlated with eye colour. Of the ten genes, they found that only four really matter. By looking at these, they can classify someone as having dark eyes (black and brown), light coloured eyes (blue and grey), or hazel eyes (greenish-brown) – with 97% certainty.

  DNAPrint is now applying exactly the same technique to hair colour, identifying possible genes and looking for SNPs. Representatives say they have made some headway and classify people into one of three groups – blonde, brown or black-haired – with some accuracy, from their DNA alone.

 

1. What is meant by a ‘crime stain’?

A traces of blood left at the scene of a crime

B DNA belonging to known criminals

C samples of blood or hair in criminal archives

D DNA samples left at the scene of a crime

 

2. Forensic scientists are interested in finding out

A if the genes responsible for criminal tendencies can be identified

B how far personal appearance can be predicted from DNA

C if hair colour could be linked to criminal behavior

D whether or not DNA can be used to identify a suspected criminal

 

 

3. What problem do scientists face in developing DNA tests for hair and eye colour?

A the fact that these characteristics are not generally determined by one gene

B the variation in test procedures required for these characteristics

C the fact that these characteristics are not necessarily related

D the variation in distribution of these characteristics from one country to another

 

SUPPLEMENTARY READING

Read and translate the newspaper article.

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