genome/ allele question

[Meredith92]

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This is gonna seem like a really stupid question... but its something I've always kind of wondered.

EK says "The genome of one human differs from the genome of another at about one nucleotide in every 1000"

But this doesnt seem to make sense to me since there are so many different types of alleles- shouldnt our dna vary more than that? I think I get confused because books normally dont talk about alleles until you get to meiosis... but when we talk about genes/the genome/replication i never see where alleles fit in.

Thanks so much and sorry this question is so dumb!

 

[amberkre]

In a human nuclear genome there are about 3200 000 000 nucleotides of DNA so if you take all of the nucleotides and assume there is a difference every 1000 of them that means there are about (3200,000,000/1000=3,200,000) 3.2 million differences in nucleotides from one genome to the next. That statistic would correlate to the multiple allele differences from one human to another. While this 1000 might seem like a small amount in the scheme of things, it actually accounts for the different alleles in a population. If you consider the fact that the humane genome is 95% identical to the chimpanzee genome, it becomes easier to grasp the idea that only a 5% difference in nucleotides equates to an extreme difference in phenotype.

At least thats how I make sense of it!

 

[Meredith92]

Great thanks! That definitely put it into perspective!