"As a general rule, more complex organisms, like humans, have larger genomes than less complex ones," said J. Todd Streelman, assistant professor in the School of Biology at the Georgia Institute of Technology and co-author of the study. "You might think this means that animals with the largest genomes are the most complex and for the most part that would be right. But it's not always true. There are some species of frogs and some amoeba that have much larger genomes than humans."
To help explain this paradox, a pair of scientists from Indiana University and the University of Oregon published a hotly-constested hypothesis in 2003. It said that most of the mutations that arise in organisms are not advantageous and that the smaller a species effective population size (the number of individuals who contribute genes to the next generation), the larger the genome will be.
"We agreed with some of the criticisms of the hypothesis that one had to remove the effects of confounding factors like body size and developmental rate," said Streelman. "We were able to remove the effects of these confounding factors and test whether genome size is adaptive."
Their test consisted of analyzing data from 1,043 species of fresh and saltwater ray-finned fish. Previous data on genetic variability had established that freshwater species have a smaller effective population size than their marine counterparts. If the hypothesis was correct, the genome size of these freshwate
Contact: David Terraso
Georgia Institute of Technology