paternity Case

Let's use RFLP technology to determine if Jack is the father of Jill's child named Payle.

In this scenario, DNA was extracted from white blood cells from all three individuals and subjected to RFLP analysis. The results are shown below:

In this case, it appears that Jack could be the father, since Payle inherited the 12.4 kb fragment from Jill and the 4.3 fragment from Jack. However, it is possible that another man with similar RFLP pattern could be as well.To be certain, several more RFLP loci would be tested. It would be highly unlikely that two men (other than identical twins) would share multiple RFLP patterns and so paternity could be confirmed.

In a different scenario, DNA was extracted from white blood cells from all three individuals and subjected to RFLP analysis. The results are shown below:

This time, it can be determined that Jack is NOT the father of Payle since Payle has a band of about 6 kb and Jack does not. Therefore, it is very probable that Payle's father is not Jack, though it is possible that Payle carries a new mutation at this locus and a different sized band was produced. What could you do as an investigator to be more certain that Jack was not the father of Payle?

Disease Status

In this example, we want to know if a person carries any cystic fibrosis (CF) alleles and if so, how many. Because CF is a recessive disease, anyonne with CF must be homozygous for disease alleles. From pedigree information, we can often determine who in this family is a carrier. However, if a couple comes to a genetic counselor, often an RFLP analysis is performed on the couple's DNA.

RFLPs are known for CF and so it would be easy to determine if a person were homozygous wild-type (wt), heterozygous "carrier", or homozygous disease alleles and thus have CF.

For couples expecting a child, it would be simple to test both parents and make a prediction about the eventual disease status of their fetus. For example, if both parents were homozygous wt, then all of their children would also be homozygous wt:

However, if both parents were heterozygous, they could have children with any of the three genotypes, though heterozygous children would be twice as likely as either of the homozygous genotypes.