<p>Why doesn't genome size correlate to organism complexity? Why do plants have a larger genome than humans? hmm? </p>
<p>PM me if you think you can help - I'd really appreciate it!</p>
<p>Thanks!</p>
<p>I really hope this isn't a homework question.</p>
<p>I think the first question here is why it's automatically assumed that "complexity" is a trait which ought to be assigned certain organisms and not others. But that's another beef for another day.</p>
<p>Plant genomes tend to be relatively gene-poor, particularly plants like maize. Maize has a great deal of noncoding DNA, mostly in the form of transposons and other quote unquote junk DNA. Genomes in many plants are like a computer that hasn't been defragmented in a while -- there's a lot of space, but the usable files are scattered around such that any given region of DNA is unlikely to contain coding DNA. Organisms like bacteria and yeast, in contrast, are quite gene-rich -- they look like they've been defragmented pretty well.</p>
<p>Another reason that the absolute number of genes doesn't correlate well with our undeniably biased perceptions of complexity is that many mechanisms create different expression patterns in different cells which are not reflected simply by examining genomic DNA.</p>
<p>Man dude, because the earth crapped 'em out that way. It just happened.</p>