<p>The only possible issue with using GRCm38 as the reference is that since GRCm37 was used in the bait design there are likely a few probes that will show artificial structural variations, due to errors in GRCm37. However, these will be present in all of your mice and if you use liftOver to look at the regions around the probes then such regions should become obvious. In fact, that'd be a convenient thing to do if you want to keep your (likely better) GRCm38 alignments, flank each probe site by a few hundred bases and then use liftOver to get the GRCm37 coordinates. If you go through the result you'll be able to find the false-positive structural variants due to the baits being designed with an older reference.</p>

<p>Alternatively, just use GRCm37 and hope that any issues with it don't result in false-negative SV calls.</p>

CC BY-SA 4.0
2018-07-04T18:20:10.210Z
I kept the GRCm38 aligned reads and used NCBI's remap tool on the target enrichment design alignment file from Roche. With the remapped target alignment file I was able to see that the exon in the middle of the GRCm38 enrichment was indeed a target! And good call on the false positive SVs being in all of the samples.
Kohl Kinning
CC BY-SA 4.0
2018-07-07T21:43:38.297Z
Can you clarify the SV issue? Regardless of how the probes are designed, wouldn't they only pull down the DNA fragments that physically exist?
burger
CC BY-SA 4.0
2018-07-04T06:57:10.660Z
2018-07-04T06:57:10.660Z
Devon Ryan
<p>I have exomes from 24 individual mice. The exomes are the product of Roche's SeqCap EZ HyperCap target enrichment kit. I see that the mouse exome design comes from mm9/NCBI37, the previous major reference genome released in July 2007. </p>

<p>Which reference should I use to align these reads? What artifacts may arise from mapping these reads designed from mm9 to the mm10 reference? I have already aligned the reads to mm10 and noticed an erroneous exon right in the middle of an intron, perhaps a target that was an exon in the mm9 release but revised out of the mm10 release. My goal is to investigate structural variation.</p>

<phylogenetics><variant-calling><reference-genome><exome>
GRCm37-designed exon target enrichment, which reference to use?
# GRCm37-designed exon target enrichment, which reference to use?

(Asked by: username_0 on 2018-07-03)

I have exomes from 24 individual mice. The exomes are the product of Roche's SeqCap EZ HyperCap target enrichment kit. I see that the mouse exome design comes from mm9/NCBI37, the previous major reference genome released in July 2007.

Which reference should I use to align these reads? What artifacts may arise from mapping these reads designed from mm9 to the mm10 reference? I have already aligned the reads to mm10 and noticed an erroneous exon right in the middle of an intron, perhaps a target that was an exon in the mm9 release but revised out of the mm10 release. My goal is to investigate structural variation.

**Tags:** phylogenetics, variant-calling, reference-genome, exome

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## 1 answers

### Answer by username_1 on 2018-07-04. Score: 2 | Accepted answer

The only possible issue with using GRCm38 as the reference is that since GRCm37 was used in the bait design there are likely a few probes that will show artificial structural variations, due to errors in GRCm37. However, these will be present in all of your mice and if you use liftOver to look at the regions around the probes then such regions should become obvious. In fact, that'd be a convenient thing to do if you want to keep your (likely better) GRCm38 alignments, flank each probe site by a few hundred bases and then use liftOver to get the GRCm37 coordinates. If you go through the result you'll be able to find the false-positive structural variants due to the baits being designed with an older reference.

Alternatively, just use GRCm37 and hope that any issues with it don't result in false-negative SV calls.

> **Comments:**
> **username_0**: I kept the GRCm38 aligned reads and used NCBI's remap tool on the target enrichment design alignment file from Roche. With the remapped target alignment file I was able to see that the exon in the middle of the GRCm38 enrichment was indeed a target! And good call on the false positive SVs being in all of the samples.  
> **username_2**: Can you clarify the SV issue? Regardless of how the probes are designed, wouldn't they only pull down the DNA fragments that physically exist?  

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