Metagenomics and pyrosequencing study DNA but the focus of each of these areas is different.
This is an approach that aims at analyzing DNA collected from the environment. This is often used to understand microbes' DNA and collect information about microbes' populations of even other populations.
This is a method to study or sequence DNA. In this method, the DNA is sequenced based on the principle of replication. This is often used to study DNA fractions.
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