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Which gene?

There may be many genes in a small section of a chromosome, just as there are usually several buildings in a street. To decide which is the gene they are looking for, scientists must look at the DNA sequence that makes up each gene. If they are looking for a gene involved in a genetic condition, then they may find differences in the DNA of that gene in an affected person.

There are several genes on a chromosome just as there are several buildings in a street. The different coloured beads on DNA fibres (right) show the order of genes on the chromosome.
US Department of Energy Human Genome Program (

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