# Population Genetics > mtDNA Haplogroups > H >  H1 - T16189C! Help !!

## hrvclv

Hi everybody. I persuaded some of "my people" to test. My son-in-law came out as H1 - T16189C!
A bit of a riddle to me. All I managed to find was that, apparently, the exclamation mark signals a "back mutation". What the heck is that ?
Is T16189C! an identified subclade of H1 ? Or does it define one ?
Can someone help me out on this ? Thanks in advance to whoever contributes.

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## eastara

I think it is connected to the Reconstructed Sapiens Reference Sequence (RSRS). FamilyTreeDNA already provides the results using RSRS , while most scientists still use the Cambridge Reference sequence(CRS). According to RSRS there is a mutation C16189T relative to the reference, which is very common among all haplogroups. However, those with the mutation H1-T16189C are considered in fact a back mutation relative to RSRS as the basic H has the C->T.
You can see the mtDNA haplogroups classification, for example on the Ian Logan site.
http://www.ianlogan.co.uk/sequences_..._sequences.htm

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## hrvclv

@Eastara
Thank you for your helpful post. I'll have one more question, though. Does it mean that H1-T16189C! is to be considered as a subclade of H1, just like H1a, H1b, etc... or is T16189C! simply an "anomaly" which can occur among various subclades of H, and therefore doesn't constitute a category as such ? For ex., can you have H1a-T16189C!, H1b-T16189C!, H2-16189C!, etc... ? I am afraid I am not proficient enough in genetics to sort it all out by myself...

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## eastara

> @Eastara
> Thank you for your helpful post. I'll have one more question, though. Does it mean that H1-T16189C! is to be considered as a subclade of H1, just like H1a, H1b, etc... or is T16189C! simply an "anomaly" which can occur among various subclades of H, and therefore doesn't constitute a category as such ? For ex., can you have H1a-T16189C!, H1b-T16189C!, H2-16189C!, etc... ? I am afraid I am not proficient enough in genetics to sort it all out by myself...


Yes, this should be considered a subbranch of H1, but why they use the back mutation, and not the normal alphanumeric labelling, I am not sure.
The position 16189 is rather unstable, and the back mutation T16189C and also the transition C16189A happen in many other haplogroups.

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## hrvclv

Thank you so much, Eastara. Contribution much appreciated.

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## Jenny1973

I did a full sequence test and it shows positive for 189C. I'm H1b1

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