Download Genetic Explanation 2: the role a specific gene defect

Genetic Explanation 2: the role a specific gene defect
A so called “warrior gene” has been linked to brain chemistry and increased
aggression; in some cases, people inherit a genetic mutation that causes a
deficiency in monoamine oxidase A (MAO-A) – so they inherit the “warrior
gene”. MAO-A is an enzyme that causes the breakdown of excess
monoamine neurotransmitters in the brain, such as noradrenaline and
dopamine.
The warrior gene is found on the X chromosome, which is why the gene is
more prevalent in men; women are protected from the faulty gene by their
other X chromosome. The warrior gene is simply a shorter, less active
version of a gene allele (an alternative form of a gene caused by a mutation)
on the X chromosome known as the MAO-A gene.
If people inherit the warrior gene they will have an excess amount of some neurotransmitters in the brain
because not enough MAO-A has been released. This excess amount of neurotransmitters predisposes the
individual to become aggressive when under stress including when angry, fearful or frustrated.
Evaluation
Supporting evidence
Four generations of males in a Dutch family inherited a defect with regard to their MAO-A gene, specifically
a mutation was identified in the eighth exon (section) of their MAO-A gene. This means they had the
warrior gene. The men with the defective gene (and not all men in the family inherited it) showed
aggressive, sometimes violent behaviour including arson and attempted rape. The men seemed unable to
regulate impulsive aggression, which was particularly marked when provoked.
Brunner tested the urine of the men in the family: the 5 men tested with the defective gene had higher
levels of chemicals that result from neurotransmitters. This indicates that the men’s MAO-A was deficient
because they had not released enough of it to break down the neurotransmitters, hence the excess levels
of the chemicals resulting from neurotransmitters in their urine.
Ground this to the explanation
Vishnivetskaya et al (2007) studied mice that lacked an MAO-A gene (these
were called the Tg8 mice) and compared them to a control group of mice
who had the gene. The Tg8 mice showed increased aggression towards
intruder m ice and increased territorial aggression, predatory aggression,
and isolation induced aggression. However, the Tg8 mice did not show an
increase in all types of aggression; for instance, they were not more
aggressive to anesthetized or juvenile male mice.
Ground this to the explanation