Monday, April 5, 2010

Genes and Evolution

Mr. Coyne states that the genes of a chimp compared to us humans are about a 1.5 percent difference. This sounds that we are very closely related to chimps, but later Coyne saids that these differences could completely alter a protein sequence (210-211). This would show that the sequences are hugely different. Could this be one flaw in how he presents his case for evolution? If our gene codes are different, how can we be descendants of these species? Every creature has a set amount of genes that separates it from another creature. What boundaries must be met in order to recognize that species are different from one another?

1 comment:

  1. Well, Andrew, you must realize that Coyne brings up a valid point on page 210, not "one flaw in how he presents his case for evolution." A 1.5% difference in our genes means that the order of nucleotides in our genome and in chimps' genome are 98.5% identical. Like you said, that sounds like we are very similar. Indeed, one can observe some similarities in our behavior and appearance by just watching members of both species interact with each other. Now, you seem hung up about how this could create a completely different protein sequence? One must keep in mind that as Coyne brings up, "proteins are typically composed of several hundred amino acids." (210) This is where all of the differences are generated. On average, 1.5 nucleotides differ between our genomes per 100 nucleotides. This probability calls for usually a couple different amino acids generated per each protein strand synthesized. And a single amino acid can determine the exact specifications for the secondary structure and tertiary structure of the entire protein, which has an effect on its overall function.
    Your next question: "If our gene codes are different, how can we be descendants of these species?" (Nowak 1) Andrew, we aren't descendants of modern chimpanzees. We diverged from a similar lineage of primates "around five to seven million years ago." (Coyne 196) This means that we have a common ancestor dating millions of years ago that we both come from, but with about 6 million years having passed since then, evolution has taken its course. Both the human genome and the chimpanzee genome has mutated, which gives rise to the difference that we see today.
    And in order to recognize species being different from each other, Mayr and Dobzhansky define species as "a group of interbreeding natural populations that are reproductively isolated from other such groups." (Coyne 172) In basic terms, two organisms aren't members of the same species if they can't reproduce to make fertile offspring.