Category Archives: Forensic Serology

Examination of Blood in Forensics

By @forensicfield


Blood is a type of biological evidence which is commonly found at the scene of crime.

Blood stains are often found at various types of crime scene, such as homicide, hit and run, assault, child abuse, rape, robbery and burglary. it also uses for DNA extraction and establishes  the paternity test.

Since the discovery of the ABO system by Land-steiner in 1900, knowledge in human blood identification has expanded tremendously.

Composition Of Human Blood

Blood is a mixture of many components:

* Cells

* Enzymes

* Proteins                            

* Water

* Inorganic substances (salts)

Blood contains 2 types of proteins which are-

  • Plasma
  • Corpuscles

The blood cells are of three main types:

  • Red Blood Cells (Erythrocytes)
  • White blood cells (Leucocytes)
  • Platelets (Thrombocytes)

Use of Blood detection in Forensic Science:

Blood is one of the most important biological traces that are often found on the crime scene. Due to valuable information it contains, it is considered to be a very important forensic tool. Analysis of different aspects of bloodstains can contribute to clarify the circumstances under which some violent crimes have been committed. Such crucial information can point criminal investigation in the right direction and help solve the crime. In some cases it can also help with legal determination of criminal offense which can lead to more accurate and more appropriate punishment for the perpetrator. It is very important to determine the sequence of events during the commitment of a violent crime involving blood.

Identification Of Source Of Blood

Foetal blood–  presence of HbF or Alpha Protein.

Blood of Pregnancy and abortion – Chorionic Gonadotropins or or Alkaline Phosphatase.

Menstrual blood– Fibrin Content, endometrial tissues.

Venous blood– dark in color, oozes gradually and no spurting.

Arterial – bright red and copious and showed spraying.

Methods For The Identification Of Blood

5 Types Of Blood Test Or Methods Occurred-

  1. Visual / Physical examination
  2. Microscopic examination
  3. Chemical Examination
  4. Spectroscopic Examination
  5. Serological examination
Visual /  Physical Examination

The search for the presence of blood at a crime scene is normally done by close visual examination.  The possibility exists, however, that blood may be present in amounts too little to see with the unaided eye, or that the blood at the scene had been “cleaned up” prior to arrival of the crime scene team. 

Fresh stains – bright in colour, turns to brown and black after some time. Fresh stains soluble in water or in saline

Ante-mortem blood Stains – Removed in scales due to presence of fibrin.

Post-mortem blood stain – changes in powdered on removal.

Microscopic Examination

Fresh blood stain in Microscope  – Erythrocytes and leukocytes.

Microscopic appearance of cells found in a stain extract may reveal other information.

If blood stains in an environment with a higher solute concentrate, water leaves the cell by osmosis and the cells shrink and change shape.

If stains are fresh it is possible to reconstitute the stain and proceed with microscopical identification of cellular components.

Chemical Examination





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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


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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