The given sentence is missing in the paragraph below. Decide where it best fits among the options 1, 2, 3, or 4 indicated in the paragraph.

Sentence: In each of the affected males, the genetic defect was located to the X chromosome in the region of p11-12.

Paragraph: The first suggested evidence of a human genetic mutation associated with aggressive behaviour came from a study in 1993. _____(1)____. Genetic and metabolic studies were conducted on a large Dutch family in which several of the males has a syndrome of borderline mental retardation and abnormal behaviour. _____(2)____. The undesirable behaviour included impulsive aggression, arson and exhibitionism. _____(3)____. A point mutation was identified in the eighth exon of the monoamine oxidase A (MAOA) structural gene which changes glutamine to a termination codon. _____(4)____.

The sentence about the defect being “located to the X chromosome in the region of p11-12” fits best after the description of the abnormal behaviour, i.e., at blank (3). The paragraph starts by introducing the study and its context, then says that “Genetic and metabolic studies were conducted on a large Dutch family…” , and next describes “the undesirable behaviour” like “impulsive aggression, arson and exhibitionism.” After explaining these behaviours, it makes sense to mention the main genetic finding about the defect’s location (the X chromosome, region p11-12), and then go into more detail that “a point mutation was identified in the eighth exon of the monoamine oxidase A (MAOA) structural gene…”.

If we put the sentence at blank (1), it would mention the chromosomal location before explaining what kind of study or family was involved. At blank (2), it would break the connection between the study introduction and the explanation that genetic and metabolic studies were done. At blank (4), it would come after the specific point-mutation detail, which should come after the broader chromosomal location. So, the only position that keeps the story moving from study, to methods, to behaviour, to chromosomal location, and then to the precise mutation is blank (3).