Home
Back to "Introduction to Stereotypic Behaviour"

 

18: Evidence of genetic control of behaviour.

Mankind have practiced the art of selection basically throughout the last 5000 years or so and anybody who knows just a little about canines knows that the different strains (or rather, breeds) differ when it comes to temper and overt intelligence.

Hunting dogs like Pointers are an intensive bred line of dogs of which some are relatively stable and others more nervous. During an experiment with selection, the researchers mated only nervous dogs with nervous, and stable with stables. It turned out that this character was inheritable and evident in F1. The thus achieved difference in lines was maintained during successive generations.

Researchers have performed breeding experiments with ordinary lab mice too. From a certain starting point it was possible gradually to breed to different lines where the first could be characterized by a Short Latency to Attack an intruder mouse (SAL) where the other showed a long time of latency (LAL). A systemic (in the body) injection of Apomorfine (a Dopamine agonist) caused the SAL line to have an increased stereotypic response compared to the LAL line.

Among rats, it has been possible to select for the tendency to engage in spontaneous stereotypies. Researchers have produced a High and a Low strain regarding this and the difference between the strains was maintained even when the stereotypies were induced using pharmaca.

When it comes to deciding how many genes is responsible for the yield following a selection experiment it is normal to encounter some problems. The methods in the genetic calculations use the phenotypical variance and since this is often large, it is hard to separate the effect of one or more genes. This is the reason it is common practice to think along the lines of "segregating units" instead of individual genes. Such units can consist of either one gene with a significant (large) effect, or several coupled genes, each with minor effects, which together are passed on as a unit.

Such calculations have produced several results of which these can be mentioned:

* The extent of exercise-wheel activity within a certain strain of mice is controlled by at least two, and probably not more than three, segregating units.

* The ease with which SIP (Schedule induced polydipsia) is induces among mice is controlled by one dominant allele.

* The metabolism of Dopamine in the mouse brain is probably genetically determined and the response towards cocaine, apomorphine and methamphetamine is certainly genetically determined.

* Some more recent publications could indicate that the tendency to perform stereotypic behaviours is heritable among bank voles, mink and African Striped mice (See here).

However, genetic variation does in practice seldom explain more than 50% of the phenotypical variation.

Next Topic: Summing up.