HL Animal: Genetics

Question 1

Aim of Cases + context

Answer 1

To study the genetic origins of aggression in mice by investigating the role of MAO-A gene

The MAOA gene codes for the enzyme which plays a key role in the breakdown of neurotransmitters such as serotonin. A mouse with a defect in the MAOA gene are more prone to aggressive behavior than their counterparts.

Question 2

Method of Cases

Answer 2

Ppts: Knock-out mice, a transgenic mouse where the gene that regulates the production of MAO-A was knocked out or deleted

Observation:
* between days 11-16, the mice showed several signs of low MAO-A: frantic running, violent shaking during sleep, tendency to bite the experimenter
* Adult males showed signs of offensive aggressive behaviour (i.e. bite wounds)

Testing: put another mouse in the same cage
* When the ‘intruder’ was introduced o the control mice, they would just sniff and engage with it
* When the ‘intruder’ was introduced to the transgenic mice, they would adopt a threatening hunched position and engage in aggressive behaviour
* The same result if intruder was female

Question 3

Findings of Cases

Answer 3

• Autopsies showed an increase in serotonin (6-9x higher than control mice), dopamine and norepinephrine in transgenic mice

Question 4

Conclusion of Cases

Answer 4

• The study showed that the genetic variation led to MAOA deficient mice that exhibited strong aggressive behaviour

MAOA deficiency is a predisposition toward aggressive behaviour (may be expressed through interaction with social and environmental factors)

Question 5

Aim of Weaver

Answer 5

To study how the type of nurturing rats receive from their mothers in early life effects the way their brain responds to stress in later life

Question 6

Method of Weaver

Answer 6

Sampling:
* two groups of rats

Method
* Group 1: made up of rats that received less attention from the mothers, but were now receiving vigorous licking and grooming from other rats.
* Group 2: made up of rats who received vigorous licking and grooming from their mothers, but were now receiving less attention.

• The stress levels of the rats were measured by placing each rat in a confined tube for 20 minutes and then recording the amount of corticosterone, a stress hormone, was in the rat after the confined tube.

Question 7

Findings of Weaver

Answer 7

• Type of nurturing did affect how they respond to stress

Less nurturing
* More sensitive to stress when their movements were restricted (by placing them in a narrow tube)
* Adrenal glands produced more stress hormone
* increased production of stress hormones was linked to a fewer number of receptors for these hormones in the brain (specifically glucocorticoid receptors)
* smaller number of glucocorticoid receptors in the brain was linked to the suppression of the glucocorticoid receptor gene
* The genetic sequences themselves did not differ, but the less nurtured rats had more chemicals that inhibited the transcription of the glucocorticoid receptor gene

• = fewer receptors produced -> more stress hormones released -> organisms suffered more consequences of stress

Question 8

Conclusion of Weaver

Answer 8

That not only can inheritance of genes affect behaviour. The environment can have an impact on genes and gene expression.