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> The human genome comprises 3,234.83 Megabases and contains ~ 19,000 genes. It has been estimated that the genomes of humans are 99.9% identical. How likely is it that any single gene might vary from one individual to another? Assume an average length for a gene of 3 kilobases. 
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Is it still 0.01%, the same as for the whole genome? Why then we have the number of genes in this exercise, together with an approximate length?