The use of Y-STR kits is important for identifying male sources in a DNA profile, especially in the presence of female DNA. Today, let’s talk about the advantages that Rapidly mutating YSTRs add to a standard YSTR kit.
To set the stage, the primary difference between standard Y’s and rapidly mutating Y’s is their frequency of mutation per locus per generation. There is a 10-100 fold higher mutation rate with rapidly mutating Y-STRs.
So, what is different about the RMY markers that cause them to mutate more frequently?
STR mutation rates are based on base composition…., number of repeats…, and sequence structure.
Keep in mind- multi-copy markers tend to mutate more rapidly.
The RMY markers have one or more of these characteristics when compared to standard Y markers.
Consider a case in which two brothers have been identified as suspects and each has accused the other of the crime. It is important in this scenario to differentiate between the two related males to identify the true perpetrator.
This is when the rapidly mutating YSTRs shine. Because of the higher mutation rate and therefore better discrimination capacity, brother pairs & in other cases, father-son can be distinguished.
The most useful YSTR kit will have a balance of standard YSTRs for kinship analysis and rapidly mutating YSTRs for familial distinctions.
Now, because of the increased discrimination capacity of rapidly mutating YSTRs, there has been discussion around incorporating these markers into autosomal STR kits to help determine the number of males in a given profile. This brings up a few key questions –
For one, how confident can you be with just one or two rapidly mutating Y markers in determining the number of males in a mixture?
Since we know duplication and deletion events occur, it would be prudent to look at a more complete profile rather than just a few markers when determining the number of contributors in any autosomal or YSTR mixture in order to prevent erroneous conclusions.
Let’s look at an example-
Here we have a single source male profile that is missing alleles at multiple markers.
The affected markers are in close proximity on the Y chromosome, leading to the conclusion that there was a large deletion spanning a length of the chromosome and affecting all markers in that location.
Using these markers to determine number of contributors could lead an analyst to underestimate the number of male contributors in a mixture.
Another point to consider is the weight of the evidence. How will statistics be applied to these locations? In order to utilize Y markers you MUST use the haplotype frequency rather than individual allele frequencies. Determining the haplotypes of multiple male contributors based on only a few YSTR markers may lead to inaccurate conclusions.
Without having confidence in the number of contributors or giving value to a conclusion with statistics, the most appropriate application to gain information on male sources is the use of a YSTR kit that includes both standard and rapidly mutating YSTRs.
That’s all we have for today. Hope this was helpful. If you have any questions or would like to see more such videos, click on the link below,
And don’t forget- when in doubt, you can always refer Back to Bases!
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