Re: Why is a frogs DNA longer than a humans?

Hi -

What you are hinting at with your question is known as the C-Value Paradox (C for "Content of DNA"). Namely, some organisms have substantially more DNA then would be expected based on their complexity. Bacteria have ~4 x 10 ⁶ nucleotide pairs per cell, most plants and animals have about 2 x 10 ⁹ nucleotide pairs per cell. However, some amphibians have 25 times more DNA than mammals.

This increase in the amount of DNA appears to be the result of a cumulative addition of small amounts of DNA. It is not due to increasing the number of chromosomes (polyploidy).

One explanation for the C-value paradox attributes the size of the nuclear genome to "junk" (typically non-coding) genetic elements that accumulate until the costs to the organism of replicating excess DNA select against it.

Hope this helps.

cheers,
gabriel

References:

• What is a Genome?
• Pagel, M; Johnstone, RA. Variation across species in the size of the nuclear genome supports the junk-DNA explanation for the C-value paradox. Proceedings of the Royal Society of London. Series B: Biological Sciences, 1992 Aug 22, 249(1325):119-24.
• Molecular Biology of the Gene. Watson et al. 1987 Volume 1 p670. Publisher: Benjamin Cummings.