Wednesday, October 06, 2004


The human-ape gene comparison has always had me confused. I know next to nothing about genetics -- which may explain the confusion -- but I'm still puzzled over this:

People say that humans and apes (or bonobos or chimps or whatever) share 98% (or 97% or whatever) of their genes.

But this statement seems ambiguous. For example, say that humans and apes have exactly 100 genes. Which of the following would be true?

1. When you line up each of the 100 genes, they all match perfectly except for 2 of them. Gene 1 of the human perfectly matches Gene 1 of the ape. And so forth. But when you get to Genes 99 and 100, they are completely different. Thus, that is a 2% difference.

2. When you line up all 100 genes, they all differ from each other by a margin of 2%, give or take. Gene 1 of the human differs by 2% from Gene 1 of the ape. And so forth. Thus, there is a 2% difference, but that difference applies to 100% of the genes.

The chart at this Panda's Thumb post seems to imply the latter. Which is it? Or is it a mixture of the two? Or does the question even make sense?


Blogger Tim McNabb said...

I remember long ago (mid 80s) hearing about the similarities between ape genes and human. I'm inclined to be skeptical for two reasons.

1)This claim came long before we started fully sequencing genes, much less before we started working out what the sequences did. I'm not sure how that 2% difference could be meaningfully known.

2) That critical 2%, assuming it is an accurate figure, may be a foolish thing to confound the wise. On a strand of DNA of 100,000 codons (the three letter 'characters' transferred by mRNA to the ribosome)you could very likely have overlapping sections of code. The section 1856 through 2422 might express an enzyme, whereas section 1923 through 3123 might be code for collegen fiber molecules. Sprinkle 2% of codons throughout the overall strand, and suddenly the two sequences may mean completely different things.

Hope I've shed a little light. It's so complicated that is defies succinct explanation, and I can hardly talk about it without needing to pause and worship God.

Tim McNabb

9:26 AM  

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