many copies of which are located in the energy-generated organelles called mitochondria. Each of the approximately 10-13 cells in the adult human body has it’s own copy or copies of the genome, the only exceptions being those few cell types, such as red blood cells, that lack nuclei in their fully differentiated state. The vast majority of cells are diploid and so have two copies of each autosome, plus two sex chromosomes, xx for females or xy for males- 46 chromosomes in all. These are called somatic cells, in contrast to sex cells or gametes, which are haploid and have just 23 chromosomes, comprising one of each autosome and one sex chromosome.In order to obtain the human genome sequence, several strategies, involving different techniques were used. These techniques involved much more than just methods for sequencing DNA molecules. These methods are obviously of paramount importance but they have one major limitation: even with the most sophisticated technology it is rarely possible to obtain a sequence of more than about 750 bp in a single experiment This means that the sequence of a long DNA molecule has to be constructed from aseries of shorter sequences. One approach would be to brake the molecule into fragments, determine the sequence for each one, and use a computer to search for overlaps and build up the master sequence. This shotgon method is the standard approach for sequencing small prokaryotic genomes, but the required data analysis becomes disproportionally more complex as the number of fragments increase, leading to much higher risks of mis-sequencing. The problem is further compounded where a repetitive sequence is broken into fragments, with many of the pieces containing the same or very similar, sequence motifs. It would be very easy to reassemble these sequences so that a portion of the repetitive regions was left out or even that two pieces of the same or different chromosomes were mistakingly connected togethe...
