Tag Archives: DNA

Y-STRs

By @forensicfield

Introduction

A Y-STR is short tandem repeats on the Y-chromosome. Y-STRs are often used in forensics, paternity, and genealogical DNA testing. Y-STRs are taken specifically from the male Y chromosome.

Y-chromosome short tandem repeats (Y-STRs), also known as microsatellites and simple sequence repeats play a valuable and important role in forensic molecular biology.

What is Y-chromosome?

It contains approximately 60 Mb of DNA, about 95% of which, termed the non-recombining region of the Y (NRY), does not undergo sexual recombination and is present only in males, being inherited from the father by his sons.

Y-STRs Markers

Unique segments of DNA at certain pre-determined locations along the Y-chromosome of each man.
Each of these locations is called a microsatellite or YSTR marker , and each one of the markers that Family Tree DNA examines has been given a name, such as DYS 458 or DYS 385a.

Why Y-STRs is use?

✔ Involvements of Males in ¦-
– 80% of all violent crime.
– 95% of all sex offenses.
✔ When trying to determine the genetic profile of the male donor in a male/female DNA admixture (when F/M > 20, often >1000) and autosomal STR analysis fails (is not informative) or not possible.
✔ Determination of number of semen donors.

What Can be Tested for extraction of DNA?

  • Sexual assault swabs,
  • Clothing,
  • Hairs,
  • Items that have been touched or handled (ex: weapons such as guns, knives, etc.),
  • Ligatures used for strangulation,
  • Stains collected from an object or surface,
  • Fingernails, etc.

Areas of Use in Y-chromosome Testing::

Future of Y Chromosome Testing:

💡 Commercial kits make Y-STRs more available and more compatible between laboratories
💡 More accurate likelihoods of Y-STR profiles can be calculated
💡 Both lineage analysis and Forensics can use Y chromosome markers
💡 Additional markers are being tested
💡 New population studies are being done

Y-STR AS PROOF OF RAPE WHEN SPERM CELLS CANNOT BE FOUND:

Identification of spermatozoa is the biological evidence most often sought in the examination of rape victims. Absence of spermatozoa usually terminates biological investigations, and the victim’s testimony can therefore be contested. We assessed the utility and reliability of PCR amplification using Y-chromosomal STR polymorphisms in specimens taken from female victims of sexual assault with negative cytology.

Advantages of Y-STR

1. The primary value of the Y-chromosome in forensic DNA testing is that it is found only in males.
2. Using Chromosome Y-specific polymerase chain reaction (PCR) primers can improve the chances of detecting low levels of the perpetrator’s DNA in a high background of a female victim’s DNA.
3. Y-chromosome tests have also been used to verify amelogenin Y-deficient males.
4. The same feature of the Y-chromosome that gives it an advantage in forensic testing, namely maleness, is also its biggest limitation.

Limitations of Y-STR

Y-STR testing cannot uniquely identify an individual.
All men from the same lineage will have the same Y-STR profile.

Case studies

Mystery Solved: The Identification of the Two Missing Romanov Children Using DNA Analysis.
Combined with additional DNA testing of material from the 1991 grave, we have virtually irrefutable evidence that the two individuals recovered from the 2007 grave are the two missing children of the Romanov family: the Tsarevich Alexei and one of his sisters.

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