Photo: Glowing fluorescent E. coli samples at GenSpace
is hard to tell because some generations ago there was neither a reliable diagnosis, nor the possibility of DNA testing or standardized treatment. Today there are services that cover the testing of several genetic defects and screen for diseases, but the costs for an individual are still remarkably high. Using basic tools In the majority of cases SMA is caused by a mutation of the SMN1 gene on chromosome 5 (we have 22 autosomal chromosome pairs that are alike in all humans and two sex-determining chromosomes: x and x or x and y). There can be a deletion of an SMN1 gene copy or a mutation in the gene which you can observe by looking at the DNA sequence of the gene, especially in exons 7 and 8. DNA sequences consist of exons and introns; exons are parts that code for a function and are later on transcribed into protein and the regions in between – ‘non coding’ but in most cases having regulatory properties - are called introns. With enough data 34
and background info about where to search for this mutation, one can carry out a so called PCR-RFLP, which is a technique that combines two key tools frequently used in a biolab. PCR stands for ‘polymerase chain reaction’ and cyclically amplifies a piece of DNA until you obtain millions of copies. RFLP is the abbreviation for restriction fragment length polymorphism and it observes the differences between two probes. Another method to cut out determined pieces of DNA and to compare them is the use of restriction enzymes. Those enzymes are small biological machineries, each specialized in cutting the sequence of DNA always on the same combination of letters (there are four “letters” used in DNA: A, C, G, T). After cutting probe A and B you can load a gel where you visualize DNA and compare it to a reference. Unfortunately I was unable to finish my experiment at GenSpace last summer. During the last few days of my stay in New York, hurricane Irene hit, which delayed the supplies I was expecting.