DNA sequences provide very important clues to the evolutionary relationships of animals. Creationism basically states that god made it that way and makes no predictions. They just say that’s how god did it. It is nothing more than an unsupported assertion.
Let’s take an evolutionary view of some genes. I randomly chose the alpha actin gene – it actually turned out to be a very good example. I compared the sequences of the first 42 amino acids between humans, chimps (predicted sequence) and mice, and they were identical. The human/chimp and mouse sequences are shown below in Red and blue respectivley (differences are highlighted by boxes).
Let’s take an evolutionary view of some genes. I randomly chose the alpha actin gene – it actually turned out to be a very good example. I compared the sequences of the first 42 amino acids between humans, chimps (predicted sequence) and mice, and they were identical. The human/chimp and mouse sequences are shown below in Red and blue respectivley (differences are highlighted by boxes).
As mentioned previously, amino acids are encoded for in DNA by codons. These are sequences of 3 nucleotides that make a “genetic letter”. The interesting thing is that more than one codon can encode a particular amino acid (leucine for example has 6 different codons). This is called genetic redundancy. So, we can predict that although the amino acid sequence might be the same, the nucleotide sequence will be similar in closely related species, and less so in distantly related species that last shared a common ancestor 10s of millions of years ago.
Looking at the DNA sequences of the alpha Actin genes, there is no difference between humans and chimps, suggesting they are closely related, but as shown above, there is a 7 % difference in the mouse sequence (yet the amino acid sequences are identical). To further illustrate the point, lets take a random part of the amino acid sequence (this part DSTALV). This is encoded in humans by the codons GAC AGC ACT GCC TTG GTG, but could just as easily be be encoded for by the sequence GAT TCT ACG CGA CTG GTA.
GAC AGC ACT GCC TTG GTG (actual sequence)Looking at the DNA sequences of the alpha Actin genes, there is no difference between humans and chimps, suggesting they are closely related, but as shown above, there is a 7 % difference in the mouse sequence (yet the amino acid sequences are identical). To further illustrate the point, lets take a random part of the amino acid sequence (this part DSTALV). This is encoded in humans by the codons GAC AGC ACT GCC TTG GTG, but could just as easily be be encoded for by the sequence GAT TCT ACG CGA CTG GTA.
GAT TCT ACG CGA CTG GTA (possible sequence)
This would give exactly the same amino acid sequence, but is 53% different to the actual sequence – that is considerably different to the mouse sequence that encodes this region (a mere 13% difference). This is not the only alternative way to write the sequence: D has 2 alternative codons; S has 6 alternative codons; T has 4, as does A; L has 6 and V has 4 alternative codons. So, if a creator wanted to leave a signature, this is where he/she/it could do so. He could make “related” organisms show very little similarity in their genes – that would mess up evolution. Instead, what we see again and again is that the closer species are phyllogenetically, the more similar their DNA sequences – evolution is the only reasonable explanation.
4 comments:
Thanks again Billy.
I understand the high level conclusion - but have to admit to be getting lost on the detail with so many letters, genes and acids.
What is meant by "predicted sequence" you used for humans and chimps and the mice?
I also got lost on the point about the amino acid sequences are identical but alpha Actin genes are different?
I assume these are completely different 'things' so why would we expect the amino acid sequences to be the same (or don't we? Is that the point?)
I got confused...
Cheers
Lee
Hi Lee,
What is meant by "predicted sequence" you used for humans and chimps and the mice?
I used the actual sequence of amino acids for the human and the mouse. The chimp protein sequence appears not to have been published, but the gene sequence has. From the DNA sequence you can tell what the protein sequence is. For example, ATG codes for methionine, ATC encodes Isoleucine and so on.......
I also got lost on the point about the amino acid sequences are identical but alpha Actin genes are different?
My next post will go into this in more detail, but as I moded with the short 5 amino acid sequence, there is more than one code that could be used to encode a particular amino acid. You can therefore vary the code letters, but keep the amino acid sequence the same - Mutations that alter codon usage are more forgiving than mutations that change amino acid usage - as this may affect protein function. So, changing ATC to ATT (which both encode Isoleucine) will not change the amino acid sequence. Changing ATC to ATG will change from Isoleucine to Methionine. So there are many ways that a piece of DNA can encode the same protein sequence. A designer could have utilised this - the two alternatives I gave are only 45 % similar. In reality though, Humans and chimps are identical, with the less closely related mouse being more different.
Thanks... makes more sense now.
Lee
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