Category Archives: Forensic Biology

Seminal fluid Analysis in forensics

Seminal fluid is a complex mixture of secretions from at least four male urogenital glands.  The seminal vesicle gland contributes approximately 60% to this mixture, the prostate gland contributes approximately 30%, and the combined contribution of the epididymis and bulbourethral glands account for the remaining 10%.

Number of Spermatozoa – 50,000 to 3,50,000.

Color – Greyish Yellow / Greyish White.

Odour – seminal odour.

pH – 7.3-7.5.

Appearance – Thick and Semitransparent,

Density – 1.028.

Semen consists of the following

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Urine Analysis


Detecting and identifying body fluids at a crime scene can provide essential information about a crime or incident and the people involved. Like other physical flood forensic experts or scientists may be asked to recognize the presence of urine in cases such as harassment, rape or murder.

Urine is a difficult bodily fluid to detect due to the sensitivity of available tests and low positive results. The nature of the fluid causes it to dilate and thin out on the surfaces of the fabric, and it makes it harder to find. Smell may be an indicator, but it will cover a whole thing and will not be local to the area with stains.

Composition of Urine

  • It is mainly composed of water with urea, organic salts, proteins, hormones and a huge range of metabolites. It generally contains about 60 parts of water and 40 parts of solid materials.
  • Urea is an organic compound that is found in higher concentrations in urine than any body fluid.
  • Creatinine is another organic compound present in high concentrations in urine.
  • Unusually it may contain sugar albumin by pigment in case of jaundice as abnormal amount of one and other of its normal component.

Visual/ Physical Examination

Following are considered as important attributes in this initial examination:

  • Color
  • Transparency
  • Turbidity
  • Odor
  • Volume
  • pH
  • Specific Gravity


  • Generally specific gravity is measured by Refractometer.
  • The specific gravity of urine is higher than water.
  • The specific gravity of urine is 1.06 to 1.0 whereas water specific gravity is 1.


4.5 – 8.5

(It is indicator of diet.)

Examination For Urine

GEE’s Methods or Urea Nitrate Crystals Test

In This Method Colorless 4 To 6 Sided Rhombic Shape Urea Nitrate Crystals Formed If Positive After Adding A Drop Of Conc. HNO3.


The DMAC (para-dimethylaminocinnamaldehyde)test is perhaps one of the most common methods for detecting urine based on the presence of urea, producing a pink or magenta color if positive.


Stain Treated With Resorcinol Reagent And CuBr2 Will Produced RedColour Which Show Presence Of Indican.


In this test chromatographic paper of stain treated with 2N NaOH followed by a drop of picric acid produced Orange/Red/Brown colour if positive.


Creatinine is another compound found in high concentrations in urine, thus a number of tests have attempted to utilise this for urine identification tests. The Jaffe test utilises picric acid which, in the presence of creatinine, forms a red compound known as creatinine picrate. The colour change is proportional to the concentration of creatinine present.


The Salkowski Test Produces A Blue Colour In The Presence Of Urine Via A Reaction Between Sodium Nitroprusside And Creatinine When Heated.

RSID (Rapid Stain Identification Series)

The immunological RSID test has also been developed for the detection of urine, based on the presence of a urinary protein known as the Tamm-Horsfall protein.

ph of body Fluids of Human

pH : pH (potential of hydrogen’ or ‘power of hydrogen’) is a scale which is used to specify the acidity or basicity of an aqueous solution.

Human Body need to maintain pH level in the serum about 7.4 to live. pH of blood is 7.4 but the pH of other Body flood is Different. Upper and Lower Part of Stomach have different pH value. Upper stomach pH value ranges from 4.0 to 6.5 while Lower Stomach pH value ranges from 1.5 to 4.0.

Following image has shown the different pH level of Different body fluids of Human Body:




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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