IB Docs (2) Team
Animal research: Genetics
Animal research and genetics
After completing this lesson, you should be able to:
- Evaluate two studies that show how animals are used to study the role of genetics on behaviour
- Explain the limitations of animal research
Before completing this section of the module, please read Animal research in genetics.
While reading this section, be sure you understand the following concepts:
- Gene-environment interaction
- MAOA
- Selective breeding
- Transgenic mice (knockout mice)
Exam tip
On your exam, the IB may ask you to discuss the usefulness of animal models in "the study of the role of genetics in behaviour." In order to answer this question, you need to do two things. First, you need to discuss the use of animal models. This is what we looked at in the first component of this module. Then, you need to be able to discuss an example. That example should look at animal or human research from the unit on genetics. Regardless of which study you choose, it is important that there be a clearly identified behaviour in the explanation of the study.
For the exam, you should be able to discuss one behaviour - so, having one animal and one human study would be enough for this exam question.
Aggression: MAOA and the warrior gene
Before beginning this section, please watch the following video on what is called the "warrior gene."
The MAOA gene provides instructions for making an enzyme called monoamine oxidase A (MAOA), an enzyme that breaks down dopamine, norepinephrine, and serotonin. Variations in the x chromosome, known as the MAOA-L, results in low levels of the enzyme - and this appears to be linked to aggressive behaviour.
Thinking about research
Read Cases et al (1995). While reading the text, fill in the chart below in your notebook. To fill in the last row of the table, read the study summary below of Caspi et al (2002).
| Researcher | Procedure (quick summary) | Findings | Limitations |
| Cases et al (1995) | |||
| Brunner et al (1993) | |||
| McDermott et al (2009) | |||
| Tiihonen et al (2014) | |||
| Caspi et al (2002) |
Caspi et al (2002) wanted to see if an interaction between a gene (MAOA-L) and maltreatment in childhood could predict antisocial behaviour in adulthood. The sample was made up of over 1000 males from New Zealand. Simply having the genetic variation did not predict antisocial behaviour. However, mistreatment in childhood in combination with the MAOA-L variant was a good predictor of antisocial behaviour. Males with high MAOA activity - in other words, they didn't have the variation - did not have high antisocial scores, even when they had experienced childhood maltreatment.
A word about mice
A knockout mouse is a laboratory mouse in which researchers have inactivated, or "knocked out," an existing gene by replacing it or disrupting it with an artificial piece of DNA. Knocking out the activity of a gene provides valuable clues about what that gene normally does. Since humans and mice share several of the same genes, observing the characteristics of knockout mice gives researchers information that can be used to better understand how a gene may cause or contribute to behaviour or disease in humans.
Exam question: Discuss the value of animal models in the study of genetics and behaviour.
Criterion B. Knowledge and understanding
Marks are awarded here for showing an understanding of animal models.
You should explain what is meant by an animal model and why researchers choose to use animals in the study of genetics and behaviour. This would include - the theory of an evolutionary continuum, the short lifespan and high reproduction rate of some animals, similar physiology of animals and humans, the ethical considerations of research on humans, and the relatively easy access to participants.
Criterion C. Use of research
Marks are awarded here for both the choice of research and its explicit link to the question.
It is appropriate to have one study with animals and one with humans in order to show how the research in animals is confirmed in human research.
You should explicitly identify the behaviour that is being studied in each study.
Noting key differences between the animal and human studies will be important for critical thinking.
Criterion D. Critical thinking
Marks are awarded here for critical thinking with regard to the question.
Do not simply evaluate the studies. Critical thinking should focus on the value of animal models. The strengths and limitations of animal models should be clearly addressed.
Thinking about research
Looking at the research in the chart above, what does this tell us about the relationship between genes and environment in human aggression? To what extent does the study by Cases (1995) reflect what we see in the other studies? What concerns would you have about using Cases' research as a model for human aggression?
In the next and final component of this module, we will look at ethical considerations. You could be asked for ethical considerations in the use of animal research in the study of genetics and behaviour. In answering this question, you would need another animal study for genetics.
Hendricks et al (2003) studied another candidate gene for aggression - PET-1. The researchers removed the PET-1 gene from male mice to see what the effect would be.
They found that the mice had heightened levels of both anxiety and aggression - when the mice were given a "territory", their response time to attack an intruder was significantly lower than a normal wild mouse, and they tended to launch an attack more often. It was also interesting to note that when the mice were given a choice of an unprotected open space and a safe enclosed space, they tended to stay in the enclosed space.
The mice with the knocked out gene did not produce adequate levels of serotonin. The researchers argue that this may explain the behaviour of people that suffer from both anxiety or depression and aggressive behaviour.
Continue to Animal research: Ethics
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