One of the challenges faced with analyzing human DNA is the small size of it. Bacterial Artificial Chromosome (BAC) cloning is a method developed to increase the size of the DNA being worked with. Human DNA is inserted in the bacterial DNA to be cloned when the bacteria divides.
A newer method became popular during the Human Genome Project. Yeast Artificial Chromosome (YAC) cloning became a key process for the research because the YAC clones were larger and easier to work with than were the BAC clones.
As early as 1989, segments of the human genome were successfully recovered using YAC cloning. By 1991, a library from human DNA was created. This was a rough picture of the human genome. Similar to the picture on the box of a puzzle, this map was able to guide researchers in piecing together the genome.
To use the YAC clones, they were made of overlapping segments of DNA. Observing where the segments overlapped helped to piece to YAC clones together into a workable map.
The Human Genome Project and Cancer 