genes change at a steady rate

[danihel]

Hi
In one documentary it was mentioned couple of times that genes do change at a steady rate and this fact is used to determine how long ago did two species diverge. I don't understand this, i mean isn't it obvious that contemporary sponges didn't undertake as many genetic transformations as humans since the Eukaryotes emerged? It also has to depend strongly on how often do organisms reproduce whether they are clones, hermaphrodites or have genders...
Can someone explain if there is any truth about what was said in the documentary?

[jonmoulton]

A change in genetic sequence does not necessarily lead to a change in phenotype. A change in a nucleic acid base at a wobble position can be completely silent in terms of the resulting amino acid sequence. In many cases swapping an amino acid for a similar amino acid causes negligible change in protein structure or function. Genetic drift can happen as the phenotype remains constrained by selective pressure.

"...isn't it obvious that contemporary sponges didn't undertake as many genetic transformations as humans since the Eukaryotes emerged?"

Why is that obvious? The phenotype is obvious, the genetics are hidden without sequencing (which is not possible as far in the past as the events you are considering).

[Darby]

DNA might mutate at a sort-of, longterm steady rate, but that's for non-gene sequences that can change without effects.

[JackBean]

The rate of mutations is really quite steady-state, but differs between particullar species and even between genes/non-genes, but also the genes are changing of course. However, not each with the same rate. E.g. histones are the most conserved proteins with only two changes between human and pea