Forensics will be able to use cat and dog hairs to help convict criminals

NEWS AND COMMENT: This is an interesting development in the world of forensic science. Until now it's been all but impossible to use cat and dog hairs at a crime scene to help identify the criminal because (1) most cat hairs do not contain a root or it is dead resulting in almost no nuclear DNA sequence and (2) domestic cats have a very small number of ancient ancestors resulting in very similar DNA and therefore it is impossible to separate one from another using, as I understand it, nuclear DNA.

However, a new method of screening uses every part of the mitochondrial DNA which enables the forensic scientist to detect tiny differences and in doing so they will be able to link a domestic cat that lives with the alleged criminal. This will help to convicted criminals.

Obviously, not all criminals live with a domestic cat but in the UK, you will find a domestic cat in 26% of the households. And in those homes, there is invariably a pile of cat and dog hair. It is one of the great bugbears of many pet owners: getting rid of it!

Now it appears that forensic scientists can actually use it and as I understand it, it works like this. The criminal lives with a cat or dog. The criminal commits a crime and leaves behind at the crime scene some cat/dog hairs that have come off his clothes and which are deposited onto the victim or other objects at the crime scene. These are collected and analysed linking the criminal with the crime scene.

Although mitochondrial DNA is less variable than nuclear DNA there is just a 3% chance that two cats share the same genetics in this regard. It will be another tool to use to help pin down the criminal.

And so, forensics will now be able to use those hairs to help convict an alleged criminal. Mark Jobling, Prof of genetics at Leicester University and the co-author of the study said that, "In criminal cases where there is no DNA available to test, pet hair is a valuable source of linking evidence, and our method makes it much more powerful. The same approach could also be applied to other species, and particularly dogs."

The other co-author of the study, Dr. Jon Wetton, also of Leicester University's Department of Genetics and Genome Biology, added that, "If the police have a case where there are cat hairs but no human DNA to link a suspect with a crime it is now likely that, using our approach, we would be able to exclude the great majority of cats as the source and demonstrate a stronger link to the suspect's cat. The approach could be applied to other species, dogs being the most relevant as their hairs are also frequently found on clothing."

The study is published online on the Forensic Science International Genetics website. The abstract (summary) in an earlier study of 2014 states that "Mitochondria DNA is often the only option for DNA analysis of shed hair."

And in that 2014 study the scientists add that analysis of mitochondrial DNA has been accepted in US criminal courts since 1996 which was the date of a murder trial concerning Henry L Polk Jnr. in Mississippi. This was the first legal proceedings in America where cat mitochondrial DNA analysis was produced as evidence.

Initially the court deemed it inadmissible but once the judge had heard the arguments it became admissible.

Mitochondrial DNA versus nuclear DNA

Mitochondrial DNA and nuclear DNA differs in the following ways:

• Mitochondrial DNA is inherited only from the mother while nuclear DNA is inherited from both parents.
• Mitochondrial DNA is circular and smaller in size. Nuclear DNA is larger in size and linear.
• Mitochondrial DNA replicates separately from the nuclear DNA and encodes for proteins that work only for the mitochondria. Conversely, nuclear DNA encodes for proteins that work for the entire cell.
• Finally, nuclear DNA is found in the cell nucleus while mitochondrial DNA is found in the mitochondria (source Bing AI).

Note: the source of this post is The Telegraph newspaper on MSN. I can't find the study online at this time to allow me to provide a link to it.

-------

P.S. please forgive the occasional typo. These articles are written at breakneck speed using Dragon Dictate. I have to prepare them in around 20 mins.

How many hairs on a domestic cat?

CONCLUSION: 68,250,000 hairs on a standard-sized cat weighing 10 pounds.

I have tried to work this out before. Perhaps it would be easier to simply read what somebody else has calculated. It is very hard to be accurate because the geometry of the domestic cat means that it is very difficult to apply some basic formulas to work out the surface area. My research indicates that there are about 60,000 pairs per square inch or 25,000 hairs per square centimetre on a normal cat.

Image by Anja🤗#helpinghands #solidarity#stays healthy🙏 from Pixabay 

I decided to work out the number of hairs on the torso of a cat which is somewhat cylindrical and then add in the legs and head and tail. Fortunately, there is an online calculator to work out the surface area of a cylinder.

Smaller or standard domestic cat

I have found a veterinary chart on the MSD Veterinary Manual website which converts cat weight to surface area. A 10 pounds cat weighs 4.54 kilograms with a surface area of 0.273 square meters or 2730 square centimeters. Multiplying 2730 x 25,000 makes 68,250,000 hairs on a 10 pound cat.

Chart showing the surface area of cats of different body weights. Source: see above.

Large domestic cat!

I worked this out from scratch because I had not found the above chart at the time.

If we say that the length of the torso of a cat is 45 cm and the radius of this imaginary cylinder is 12.7 cm, the total surface area works out at 4662 cm². If we multiply that number by 25,000 (the number of hairs per square centimetre on a normal) we come to the grand total of 116,550,000 hairs on a standard domestic cat excluding the head, legs and tail.

I'm going to estimate that the area of all four legs is about 250 cm². The head has a radius of about 5 cm and if we take the head to be a sphere, which is not but it is near as I can get when working out the surface area, my online calculator makes that 314 cm². If we add that to the legs, we get 564 cm² which we then multiply by 25,000 to make 14,100,000. We then add that to the number of hairs on the torso to make 130,650,000 hairs on a normal cat's body.

I am now going to try and measure my cat to make sure that the length of his torso is as I have stated! Result: my cat is about 35 cms long on the torso. Can't measure the radius! Surprised?