The study of inherited characteristics that affect behaviour. This can be achieved by a number of methods, including breeding studies, inbreeding studies, strain and race comparisons, segregation analysis, diallele crosses, and DNA studies.
In breeding studies, the investigator controls the system of mating, and selects those animals to be mated on the basis of the presence or absence of some particular phenotypic trait. This type of artificial selection has been used for centuries for the improvement of domestic animals. When a trait is controlled by a single gene with only two alleles, selection for the recessive allele can be completed within one generation. Selection for the dominant allele takes longer. In the fruit-fly (Drosophila melanogaster) there is a sex-linked mutant yellow gene. Males with this gene are less successful in mating with wild-type females than are wild-type males. The yellow males have an altered courtship pattern that reduces their mating success. They are less stimulating to the females because their courtship contains a smaller proportion of wing vibration.
Inbreeding is a special form of artificial selection in which closely related individuals are mated. It provides a means of increasing the genetic homogeneity of a population. Different inbred lines known to be genetically unalike can be compared and analysed for phenotypic differences. Comparisons of inbred strains subjected to a range of environmental treatments yield data on heredity–environment interactions. For example, rats (Rattus norvegicus) can be selectively bred for their ability to solve maze puzzles. When such animals are raised in an impoverished environment, there is little difference between the maze-bright and maze-dull strains. Both perform badly. When raised in a normal environment, the maze-bright strain performs well and the maze-dull strain performs badly. When raised in an enriched environment, both strains perform well.
Many of the data that have been gathered in behaviour–genetic studies come from comparisons of inbred strains of different races occurring in nature. For example, different breeds of dogs (Caninae) differ in behaviour as well as physical characteristics. These differences can be studied by cross-breeding experiments, the results of which are compared with what would be expected under various genetic hypotheses.
The heritability of behaviour is measured in terms of the variance in phenotypic traits within a particular population. The heritability of a trait is the fraction of the observed variance that is due to differences in heredity. It can be studied by looking at differences in closely related animals raised in different environments, and at differences among animals raised in the same environment. In recent years it has been possible to compare the DNA of different specimens.
Subjects: Psychology — Zoology and Animal Sciences.