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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).

Solution

✅ Correct Option: 3

The missing sentence locates the defect on the X chromosome in the affected males. This naturally sits after the behaviour of the affected males has been described and just before the specific point mutation in the MAOA gene is named, that is, at blank (3). It bridges the behavioural description and the precise molecular finding. The correct choice is the one indicating Option 3.

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