PDA

View Full Version : Can a man's STRs change during his life?



MitchellSince1893
04-04-2015, 10:06 PM
Quick question for those in the know.

A male is born with a collection of specific alleles aka short tandem repeats (STR); collectively known as a haplotype.

Can the STR values change during a man's life, or do they stay the same from birth to death?

For example a male is born with the same 12 maker values as his father i.e. genetic distance of 0.

He then has a son who has 11 of 12 makers the same, but 1 has mutated so the father and son have a GD of 1.

Did the mutation occur in the father after he was born and he passed it to his son; or did the mutation in his son happen during conception?

Or are both scenarios possible?

VinceT
04-05-2015, 01:22 AM
They can change - every cell division can introduce both SNP and STR copy errors. But this happens differently in every cell. Generational changes are made manifest by the mutations that are transmitted to germline gamete cells. It had been observed however, that different tissues can exhibit different mutations comparison. This I think, is easily explained by copy errors introduced during embryonic development.

So it is possible that DNA tests conducted from buccal cells can show slightly different results from DNA tests from blood or other tissues or fluids.

Also see http://en.wikipedia.org/wiki/Chimera_%28genetics%29 for a different scenario.

But within the same tissue, since all cells are essentially being copied, any mutations are usually obscured and are random-ishly distributed. Most if not all are simply below the noise threshold for detection.

But in the case of your question: the sperm that fused with the egg that became the zygote for the first son, had no STR differences from the prevalent state observed in the father. The later sperm that became the second son, had the one. A following third sperm might be the similar to the first. The "mutated" second sperm may have come from a mutated spermatogenic factory cell in the father's testes. [Of course it should be mentioned that the first sperm was also "mutated", but was not detected because the mutation didn't involve any of the 12 STR markers (of over 400) being tested.]

So, pre- or post-conception, either during gamete cell production or during the initial zygote formation, are usually the critical points for generational mutational differences to become manifest.

MitchellSince1893
04-05-2015, 04:21 AM
They can change - every cell division can introduce both SNP and STR copy errors. But this happens differently in every cell. Generational changes are made manifest by the mutations that are transmitted to germline gamete cells. It had been observed however, that different tissues can exhibit different mutations comparison. This I think, is easily explained by copy errors introduced during embryonic development.

So it is possible that DNA tests conducted from buccal cells can show slightly different results from DNA tests from blood or other tissues or fluids.

Also see http://en.wikipedia.org/wiki/Chimera_%28genetics%29 for a different scenario.

But within the same tissue, since all cells are essentially being copied, any mutations are usually obscured and are random-ishly distributed. Most if not all are simply below the noise threshold for detection.

But in the case of your question: the sperm that fused with the egg that became the zygote for the first son, had no STR differences from the prevalent state observed in the father. The later sperm that became the second son, had the one. A following third sperm might be the similar to the first. The "mutated" second sperm may have come from a mutated spermatogenic factory cell in the father's testes. [Of course it should be mentioned that the first sperm was also "mutated", but was not detected because the mutation didn't involve any of the 12 STR markers (of over 400) being tested.]

So, pre- or post-conception, either during gamete cell production or during the initial zygote formation, are usually the critical points for generational mutational differences to become manifest.
Thanks for your response. I somewhat follow what you are saying, but let me ask it a different way.

My father was 24 when I was conceived. He was 50 years older when he took the 111 marker test. If he had taken a 111 marker test back then, would the alleles have the same values as they do 50 years later? Or would they potentially be different?

I'm interested in this question because I've assumed my father's rare DYF395S1=11-15 was passed to me, but is it possible this mutation happened after I was conceived? Yes I know I can pay and get a test to get my own STR values...but I'm curious if this is even a possibility.

VinceT
04-05-2015, 09:50 PM
Thanks for your response. I somewhat follow what you are saying, but let me ask it a different way.

My father was 24 when I was conceived. He was 50 years older when he took the 111 marker test. If he had taken a 111 marker test back then, would the alleles have the same values as they do 50 years later? Or would they potentially be different?

I'm interested in this question because I've assumed my father's rare DYF395S1=11-15 was passed to me, but is it possible this mutation happened after I was conceived? Yes I know I can pay and get a test to get my own STR values...but I'm curious if this is even a possibility.

It's highly unlikely, if both tests were conducted from your father's buccal cells. The reasoning: the entire tissue cell population of the inside of your father's mouth would have to be replaced from the single source cell having the mutation. If the swab was taken from the inside of only one cheek, I suppose there is a small chance that this effect could be observed. But by FTDNA's recommendation, a buccal swab should be scrapped from both cheeks to eliminate the chance observation of this phenomenon. Copies of the mutated buccal cells would need to replace the non-mutated cells tissues comprising both cheeks, such that the percentage of mutated cells versus non-mutated cells exceeds the call limit of homozygosity, which I recall needs to be somewhere greater than a 70-30 split.

Can the entire buccal tissue comprised of millions of cells be replaced from a single mutated source (stem?) cell within 50 years? [Well, I suppose it could, if said cell was also cancerous - i.e. exhibiting an abnormal division rate that overwhelms or kills the other non-mutated cells.]

FTDNA's lab director would need to comment on what their procedure is if an STR allele shows heterozygous dual peaks on the trace, but I believe they would re-run the test until a clear single peak is observed, or ultimately discard the sample vial as potentially contaminated.