Lea et al reported that the MAOA Warrior gene is found in about what fraction of men?

Lea et al reported that the MAOA Warrior gene is found in about what fraction of men?

• A. About one third
• B. All men
• C. None
• D. Half

Answer: (A)

The key idea is that this is about how common a gene variant is in a population, especially for a gene on the X chromosome. The MAOA gene sits on the X chromosome, so men have only one copy. If that single copy carries the low-activity variant often labeled the Warrior gene, it will influence enzyme activity directly. Lea and colleagues reported that this low-activity variant is found in about a third of men in their sample. So, it’s a fairly common polymorphism but not universal or absent—roughly 30% of men carry it. Keep in mind that having this variant doesn’t deterministically cause aggression; its effects are shaped by environment and other factors. The other options don’t fit because they imply universality, absence, or a much larger proportion, which isn’t supported by the population data.

The key idea is that this is about how common a gene variant is in a population, especially for a gene on the X chromosome. The MAOA gene sits on the X chromosome, so men have only one copy. If that single copy carries the low-activity variant often labeled the Warrior gene, it will influence enzyme activity directly. Lea and colleagues reported that this low-activity variant is found in about a third of men in their sample. So, it’s a fairly common polymorphism but not universal or absent—roughly 30% of men carry it. Keep in mind that having this variant doesn’t deterministically cause aggression; its effects are shaped by environment and other factors. The other options don’t fit because they imply universality, absence, or a much larger proportion, which isn’t supported by the population data.