>> so we've known for a long time ifyou look at o people nd exmine eir genomthere is wl be cnges or differences in the letter code of d.n.a. one particular position. we've known that for a long time. what we've now found out through high resolution genomic studys is the fine structure of chromosomes also varies between people. so in everybody cell we have 23 pairs of chromosomes-- one from mom, one from dad. and that carries our genome. and because we have one from mom and one from dad up until recently the thinking wa that tt met had two copies of every section of the genome in every gene. so you'd have one for from mom and one from dad. that was the dogma. again, as we then developed the ability to look very carefully at the d.n.a. what we found is that that was not the case at all. so you can take a look at the very fine structure of a chromosome and when you hone in what you'll find is there's a section of d.n.a. that would typically be present in one copy on a chromosome but sometimes that duplicates. it would have copies on one chromose a anothern ather chmosome. so many people are walkin