About dna question? ?

Question

the A-T, G-C ratios in DNA of cattle and rat are very similar, would the tRNA,rRNA and mRNA of these two species to be similar too. why?

Answer 1

The adenine, guanine, thymine, and cytosine ratios don't have much to do with the question. Most genomes are so large and so full of junk that I would be surprised if the ratios for any two organisms are very different.

The tRNA, rRNA, and mRNA of cattle and rats are pretty close to identical for two reasons. First, the Artiodactyls (including cattle) and Rodents (including rats) have a common ancestor that lived about 85 million years ago which is a pretty short time in evolutionary terms. For comparison, you have to go back 310 million years before the mammal line meets non-mammals in the tree of life.

The second reason is that the basic nucleic machinery is extremely "resistant" to evolutionary change because it is so vital to the operation of life. That is, any slight variation in these molecular machines is almost certain to be less effective thus highly likely to be selected against. There is other cellular machinery that is so vital to living cells that our version of the molecules is almost identical to those in pea plants.