DNA-Analytik

Dr. Holger Klapproth

���Forensik

War Herr Bin Laden wirklich der Täter ?

Dem Täter auf der Spur��� Forensik und DNA-Analytik

Romanov Mystery Solved Romanov Mystery Solved Skeletons found in a shallow grave in Ekatinerinberg, Russia, in July 1991 were tentatively identified as being the remains of the last Tsar, Tsarina and three of their five children - the Romanov family. It is believed that shortly after the night of 16th July 1918, Tsar Nicholas II, his wife Tsarina Alexandra and their five children Olga, Tatyana, Maria, Anastasia and Alexei were executed by the Bolsheviks.

Using samples taken from the surviving bones, the FSS performed DNA based sex testing and Short Tandem Repeat (STR) analysis, the results of which confirmed that a family group was present in the grave. In addition, a further testing technique wasemployed analysing mitochondrial DNA (mtDNA). Mitochondrial DNA is a tiny amount of the total DNA present, and can therefore be used when samples are too small, old or degraded for analysis by normal means. Where there is no body fluid or tissue available Mitochondrial DNA can be taken from bone. MtDNA is more likely to survive for prolonged periods than chromosomal DNA and is particularly suited to tracing maternal inheritance and testing relatedness if there are several generations between ancestor and living descendant. Following this extensive analysts, the FSS concluded that the bones found are those of the last Tsar and hisfamily.

VNTRs, was macht uns alle so leicht unterscheidbar

Was sind VNTRs

•  Variable Number of Tandem Repeats •  Kurze DNA-Sequenzen die sich im Genom befinden,die

bei fast allem Menschen aus einer unterschiedlichen Anzahl an identischen Untereinheiten bestehen

•  VNTRs unterscheiden einzelne Individiuen, aber nicht eineiige Zwillinge und nicht sicher normale Geschwister.

Beispiel für die Verteilung von drei VNTR Allelen in sechs Individuen

VNTR alleles are hypervariable regions of human DNA that differ from each other in:

VNTR stands for "variable number of tandem repeats"

A tandem repeat is a short sequence of DNA that is repeated in a head-to-tail fashion at a specific

chromosomal locus. Tandem repeats are interspersed throughout the human genome. Some sequences

are found at only one site -- a single locus -- in the human genome. For many tandem repeats, the

number of repeated units vary between individuals. Such loci are termed VNTRs. One VNTR in

humans is a 17 bp sequence of DNA repeated between 70 and 450 times in the genome. The total

number of base pairs at this locus could vary from 1190 to 7650.

VNTRs are detected as RFLPs by Southern Hybridization The most common forensic method to characterize VNTRs is using Southern Hybridization. If the DNA flanking a VNTR is cut with a restriction endonuclease, the size of the resulting DNA fragment can vary, resulting in RFLPs, or "restriction fragment length polymorphisms". This is shown diagramatically in the figure, where the red boxes represent the repeat unit and the blue lollipops represent cut sites for a restriction endonuclease. In this diagram, only three different variants (alleles) are illustrated for the VNTR locus, but 50 or more different alleles are often found at human VNTR loci.

Endonukleasen können mitten im DNA-Molekül schneiden manche Endonukleasen haben eine klare Erkennungs- sequenz: Restriktionsendonukleasen Typ II z.B. NNNNNGGATCCNNNNNN NNNNNCCTAGGNNNNNN

NNNNNG GATCCNNNNNN NNNNNCCTAG GNNNNNN

Palindrome

z.B. 5´ NNNNNGGCGCCNNNNNN 3´ 3´ NNNNNCCGCGGNNNNNN 5´

Die Sequenz liest sich auf beiden Strängen in 5´-3´, bzw 3´-5´-Richtung gleich.

Welches der Untersuchten

Kinders stammt von der

untersuchten Mutter

und dem untersuchten

Vater ?

DNA-Analyse zur Identifizierung eines Täters Ist der Angeklagte schuldig ??? Der Angeklagte wird vor Gericht beschuldigt eine Frau vergewaltigt zu haben. Direkt nach der Tat wurden von Gewebeabstriche des Opfers entnommen und das darin enthaltene Sperma gewonnen. Mit der DNA aus dem Sperma wurde eine DNA-Analyse durchgeführt. Wenn der Angeklagte der Täter war, muss sein Allelmuster mit dem des Täter überein- stimmen.

Ist Herr X schuldig

The frequency of the occurrance of different VNTR alleles in many different populations of racially and ethnically diverse peoples have been determined. The chance that an individual might have a particular pattern of 2 VNTR alleles is given by the expression 2pq, where p and q are the frequencies of the two alleles in the reference population. If p is 0.1 (10% of the reference population) and q is 0.05 (5% of the reference population, then the frequency of the DNA profile is 0.01 (or 1% of the reference population).

Mit welcher Wahrscheinlichkeit ? Imagine that a DNA forensic scientist determined that DNA from semen from a vaginal swab of a rape victim matched the DNA profile of a suspect at 5 different VNTR loci. Assume that the frequency of the DNA profiles for the 5 individual loci were 0.01, 0.02, 0.06, 0.10, and 0.03. How common or rare would this 5 locus DNA profile be in the reference population? In most cases, a "product rule" calculation can be done by multiplying each individual probability together. Thus the frequency of the profile is 0.01 x 0.02 x 0.06 x 0.10 x 0.03 = 3.6E-08. Another way to express this probability is take the recriprocal of this number, 1/3.6E-08 = 27.8 million. The DNA analyst could report that the DNA profile that is shared by the suspect and the evidence might occur by chance in 1 person out of 27.8 million. The jury could use this information to evaluate whether the match of DNAs might have occured by chance.

Und wo ist der Pferdefuß

•  Die Technik funktioniert in homogenen Populationen nicht sehr gut

•  Was ist mit Geschwistern ??? •  Auch die PCR macht Fehler •  man braucht DNA-Material •  allerdings: der Nachweis der Unschuld ist relativ sicher