Y -Chromosome is one of the sex chromosomes present in humans. Y -chromosome is a sex determining chromosome and is passed from father to son. Y Chromosomal DNA is specific to males and inherited through male descendants by genealogical mutation without any recombination.
Y Chromosomal STR typing is a method to differentiate and detect male DNA. Y chromosomal STR typing is extremely useful where female-male DNA mixtures are present and male DNA can be analyzed from the bite marks, fingernail scrapings, touch samples (especially in sexual assault or rape cases).
RELATIVE POSITIONS OF 23 Y-STR MARKERS
The combined information available from autosomal STR loci and Y -STR loci are used in solving sexual assault cases. Differential extraction doesn’t work in certain instances when there is a large difference between the male and female DNA if the DNA is present in fingernail scrapings and also in saliva samples. In such cases, the information from Y -STR loci (male-specific marker) is very valuable and aids in solving cases.
Currently, a panel of 17 evaluated markers is practical in use (Table.1). Available STR kits contain between 9 and 17 loci and all of which consist of recommended core STR loci.
Y-STR loci information played a crucial role in the abduction, sexual assault, and murder of a 5-year-old kid Samantha Runnion in 2002 (https://www.cbsnews.com/news/dna-key-in-child-murder-trial/). After 24 hours of abduction, she was left in the road and was nude. A mixture of DNA was found in her fingernails and the level was low.
Image Source – https://cbsnews1.cbsistatic.com/image515312x.jpg
Slide Courtesy -Dr. Bruce Mccord
The main disadvantage in this approach is that when a crime sample matches the suspect Y- STR loci, the paternal relatives of the suspect cannot be excluded from the crime. The combination of information from autosomal STR loci and Y- STR loci can exclude the paternal relatives of the suspect from the crime.