Which of the following represents a direct exclusion in paternity testing?

In paternity testing, a direct exclusion refers to a situation where the genetic markers of the potential father do not match with those of the child in such a manner that it is conclusive the man is not the biological father. The presence or absence of specific blood group antigens can provide this information.

In this case, the genetic markers being considered are the phenotype combinations. The scenario represented by Fy(a+b+) and Fy(a+b-) indicates a situation where the child exhibits the Fy(a) antigen and one parent exhibits both the Fy(a) and Fy(b) antigens, while the other parent displays only the Fy(b) antigen. Since the child has one marker present (Fy(a)) that neither parent could provide, this directly excludes the male as the father.

Other options involve blood group phenotypes where the combinations do not provide a direct exclusion. For instance, the A O AB option could imply that there’s a possibility of paternity if the child has the A phenotype; thus, it does not lead to a direct conclusion that the man is excluded. The M M MN combination does not conclusively exclude paternity because both the men can produce children with an MN type as well. Similarly, the R1R1 R1R1