By using these techniques, three RFLP's were discovered for CF; Doc RI, J3.11, and Met. Utilizing in situ hybridization, scientists discovered the CF gene to be located on the long arm of chromosome number seven. Soon after identifying these markers, another marker was discovered that segregated more frequently with CF than the other markers. This meant the new marker was closer to the CF gene. At this time, two scientists named Lap-Chu Tsui and Francis Collins were able to isolate probes from the CF interval. They were now able to utilize to powerful technique of chromosome jumping to speed up the time required to isolate the CF gene much faster than if they were to use conventional genetic techniques.3In order to determine the exact location of the CF gene, probes were taken from the nucleotide sequence obtained from chromosome jumping. To get these probes, DNA from a horse, a cow, a chicken, and a mouse were separated using Southern Blot electrophoresis. Four probes were found to bind to all of the vertebrate's DNA. This meant that the base pairs within the probes discovered contained important information, possibly even the gene. Two of the four probes were ruled out as possibilities because they did not contain open reading frames which are segments of DNA that produce the mRNA responsible for genes.
The Northern Blot electrophoresis technique was then used to distinguish between the two probes still remaining in order to find out which one actually contained the CF gene. This could be accomplished because Northern Blot electrophoresis utilizes RNA instead of DNA. The RNA of cell types affected with CF, along with the RNA of unaffected cell types were placed on a gel. Probe number two bound to the RNA of affected cell types in the pancreas, colon, and nose, but did not bind to the RNA from non-affected cell types like those of the brain and heart. Probe number one did not bind exclusively to cell types from CF affected areas like probe number two did.
