Slightly too high 260:280 and 260:230 ratios from gDNA extraction - Should I care? (Aug/25/2010 )

We have recently extracted genomic DNA from fish fins and in addition to very high nucleic acid yields we also measure OD ratios slightly higher than 2,0 (Nanodrop). 260:280s are in general between 2,0 and 2,1 while 260:230s are between 2,0 and 2,25.

the general rule is that ratios should be above 1,8 but what when they are higher than 2,0? The next step is SNP genotyping, should I care about these ratios or should I just be happy that they are above 1,8 and carry on?

If the absorbance curves look okay (smooth curves with valley at 230 and peak at 260), the DNA should be fine. Very pure nucleic acid will give ratios the range you reported. Some polysaccharides absorb near 260 and this may be noted by a broad 260 peak or bulges in the curve near 260; the solution may also be cloudy or slightly viscous or slightly gelatinous. This website has examples of what contamination may look like:

http://www.biomedicalgenomics.org/RNA_quality_control.html

Thanks for your reply. The absorbance curves look great so I will definitly carry on with downstream applications.