Question on Hemimethylation

[sonia29]

I'm a college sophomore and I'm looking into DNA methylation, especially how it is maintained through cell generations. I've been doing some research online and from that it seemed to me that scientists had a pretty good idea of how to accurately detect methylation patterns. However, I came across an article titled "

Cooperativity between DNA Methyltransferases in the Maintenance Methylation of Repetitive Elements" which claimed that until their experimental design,

no method to analyze the levels of hemimethylation at individual regions in the genome existed. This did not seem to match up with the rest of my research; how can the accuracy of maintenance methylation after DNA replication be measured, and how could experiments be conducted on the methylation of specific sites, if even hemimethylation could not be detected? Did those previous methods involve a lot of assumptions and generalizations? Here's a link to the article:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC139739/?tool=pubmed

Thanks!