Hi Xingyi,

GC Percent is computed based on the standard DNA base pairs (A,C,T,G) and not 
off of M,R,W,S,Y,K,V,H,D,B,X which you described below.

Do you have the "Base Position" track in "full" display mode? When you are 
zoomed in at the base level and have the "Base Position" track set to "full" 
you can see that the first line shows the DNA bases that are used in the GC 
percent computation. Below that the track shows three frames of translation 
when viewed at the base level. To read more about this track: 
http://genome.ucsc.edu/cgi-bin/hgTrackUi?c=chr21&g=ruler

Hopefully this makes sense. If not, feel free to contact the mailing list with 
any further questions you may have.

Vanessa Kirkup Swing
UCSC Bioinformatics Group


----- Original Message -----
From: "WOO Xing Yi" <[email protected]>
To: "Vanessa Kirkup Swing" <[email protected]>
Cc: [email protected]
Sent: Sunday, June 20, 2010 7:38:26 PM GMT -08:00 US/Canada Pacific
Subject: RE: [Genome] hg18 gc5Base

Hi Vanessa,

Thanks for your reply.

Another question: Other than A,C,G,T and N, how does the GC-content computation 
considers bases M,R,W,S,Y,K,V,H,D,B,X?

Thanks
Xingyi

-----Original Message-----
From: Vanessa Kirkup Swing [mailto:[email protected]] 
Sent: Saturday, June 19, 2010 5:12 AM
To: WOO Xing Yi
Cc: [email protected]
Subject: Re: [Genome] hg18 gc5Base

Hi Xingyi,

The reason for numbers other than 0,20,40,60,80,100 is because N bases aren't 
counted.  So for instance, ACTNN would yield 33.3% G-C because only 1/3 are G-C 
instead of 1/5.

Please don't hesitate to contact the mailing list if you have more questions.

Vanessa Kirkup Swing
UCSC Genome Bioinformatics Group

----- Original Message -----
From: "WOO Xing Yi" <[email protected]>
To: [email protected]
Sent: Thursday, June 17, 2010 9:12:50 PM GMT -08:00 US/Canada Pacific
Subject: [Genome] hg18 gc5Base

Hi,

I'm looking at the data downloaded from 
http://hgdownload.cse.ucsc.edu/goldenPath/hg18/gc5Base/

While it's mentioned that the possible values for GcPercent is 
0,20,40,60,80,100, I found other values as well. How should I interpret these 
values?

e.g. in chr1
307581  33.3
511231  50
3895126 50
13429746        25
29750666        50
103636491       25
103843836       33.3
103893836       50
120498676       50
120738216       33.3
120788216       50
121186956       50
141476956       33.3
141909281       25
142134336       25
142386046       33.3
142436046       50
142935836       33.3
142985836       50
143163101       25
143522081       50
144876006       50
144926006       33.3
146492661       50
146542661       33.3
146727981       50
146777981       33.3
147000771       25
147221081       25
147726266       50
204498841       25
221814466       50
246974831       33.3
247024831       50
247199716       50

Thanks and regards,
Xingyi
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