Before going to the details of the question let me post a few other details- (I posted something similar and got no useful answers-probably because I didn't explain things properly or something else)- 1. My background is not genetics. 2.I am not interested in knowing how dna sequencing or genotyping is done. 3. I am interested just in the nature of the results as in-https://en.wikipedia.org/wiki/DNA_sequencing#/media/File:Radioactive_Fluorescent_Seq.jpg Now coming to the question- Humans have two sets of chromosome in each cell. So if I say sequencing chromosome1,what does that actually mean? Which of the two chromosome's gets sequenced? Of genotyping-do comparison take place between two+two=four chromosome1's? Or is my entire undertanding flawed?