Genetic basis of behaviour

Animal behaviour is any activity performed by an animal in response to an internal or external stimuli or combination of both. Every behaviour of animal is more or less controlled by a genetical component. Some behaviours are controlled by a single or a few genes. Other behaviours are controlled by a set of genes through complex interplay.

1. Genetic basis of behaviour Janmoni Borah Barnagar College Sorbhog, Barpeta

2. Introduction Although genes may play a role in many behaviours, they never determine them. There are no genes that directly code for a behaviour-genes only codes for proteins. However, it is clear that a change in a single protein can cause a host of downstream effects and even may bring about a distinct phenotypic. The external environment exerts a strong influence on how all genes are expressed in behaviour via a development of nervous and hormonal mechanisms. The phenotype (i.e., the observable characteristics of an organism) emerges from an interaction of its genotype (i.e., the organism’s genetic composition) with environmental factors. I other words, genes via there influences on morphology and physiology create framework within which the environment acts to shape the behaviour of an individual animal. Genes also create a scaffold for learning, memory and cognition- remarkable mechanisms that allow animals to acquire and store information about their environment for use in shaping their behaviour.

3. The involvement of genes in determining animal behaviour can be simplified by the following sequence: Genes Production and activity of enzymes Regulations of biochemical reactions Regulation of functions of muscular, nervous and endocrine system Regulation of behaviour

4. Methods of studying genetic basis of behaviour Studying genetically uniform Population: A widely used method has been to genetically uniform populations of lab animals through inbreeding procedures. All the members of a given strain have the same genotype and will behave similarly if reared in the same environment. However if two groups of different strain are raised together under exactly the same environmental condition, the two lines will usually differ behaviourally on almost any test. Mice with different genotypes differ in speed with which they learn to avoid an electric shock and, in their ability, to retain learned information. Because their genotype is different, therefore their behaviour is different. This indicates behaviour is regulated by gene .

5. Simple crossing over experiments: Another way of studying genes and their influence on behaviour is hybrid study. The behaviour of hybrids has been studied in a large number of species from various animal groups—especially ducks and geese, pigeons, parrots, finches and several species of fish and insects. The behaviour of hybrid is usually intermediate between the respective parents. Male hybrids from the cross of a ring-necked pheasant and a domestic chicken, show a posture when crowing that is exactly intermediate between those of the parent species.

6. Geographically distinct populations: Geographically distinct populations often have different morphology and behaviour reflecting adaptations to the existing ecological conditions in their respective habitats. Arnold (1981) observed two populations of Garter snakes ( Thamnophis egans ). The inland population which was very aquatic, fed mainly on frogs, fish and leeches. Coastal population was terrestrial and fed mainly on slugs. Arnold found that interbred forms demonstrated an intermediate preference for slug eating.

7. Pleiotropy and polygeny : When a single gene has an effect on the expression of two or more phenotypic traits, it is said to be pleiotropic effect on the traits. . For example, testosterone controls the development of secondary sexual characters and also relates to behavioural trait like aggression. When two or more genes are responsible for a single trait, the phenotypic trait is said to be governed by polygenic factor. For example, growth is undoubtedly caused by a number of genes that act in a complex cascade. Body size is also a polygenic trait.

8. Behaviour patterns under the influence of a single gene All traits under the control of a single gene are rare and often deleterious. However, there are certain well studied genes, which cause visible alteration in the physical appearance and change in the behaviour. I n phenylketonurics p erson suffering from phenylketonuria have low I.Q and lighter pigmentation. It is an inherited disorder that increases the level of a substance called phenylalanine in the blood. It is an amino acid. It is an autosomal recessive disorder caused by mutations in both alleles of the gene for phenylalanine hydroxylase (PAH), found in chromosome 12. A notable example of the universality and specificity of single behavioural genes is provided by the period gene and other genes that regulate circadian behaviours; these were first identified through induced mutations in Drosophila melanogaster and were then found in human too.

9. Effect of multiple genes on behaviour of animals One of the most notable examples of two genes controlling a behavioural pattern is the hygienic behaviour of honey bees. Hygienic behaviour in honey bees is a heritable trait of individual workers that confers colony-level resistance against various brood diseases. Hygienic workers detect and remove dead or diseased brood from sealed cells. Rothen Buhler (1964) carried out a cross between two strains of honey be to investigate the genetical basis of hygienic behaviour. In this study two sets of bee colonies were used; in the first set the bees were designated as hygienic, i.e. the worker bees removed the dead larvae. With the second set no hygienic behaviour was observed

10. The results indicated that the genes for hygienic behaviour were recessive and that possible two loci were involved. One locus controlled the uncapping of brood cells containing diseased pupae, whilst the second locus controlled the removal of the cell contents. The investigation proposed that the queens of the bees showing hygienic behaviour were homozygous for these recessive genes. One gene named 'u' uncapping the brood; the other gene named 'r' was responsible for the bees removing the brood from the cell. Unhygeinic strain (contains dominant genes) Gene U= do not uncape the cell Gene R= do not remove the dead from Genotype=UURR Hygienic strain (contains recessive genes) Gene u= uncap the cell Gene r= remove the dead/diseased body Genotype= uurr

11. UURR X uurr Gametes UR x ur UuRr F 1 Progeny All the F1 animals were found to be non-hygienic, though they were carriers of the hygienic genes.

12. When a test cross was performed between f1 and double recessive parent ( uurr ), the following results were obtained: UuRr X uurr UR Ur uR ur ur Uurr uurr UuRr Test Cross uuRr Gametes

13. Results UuRr = Unhygienic uuRr -=Uncap the cell but do not remove the larva uurr = hygienic, both uncaps the cell and removes dead larvae. Uurr = Will not uncap, but if the experimenter uncaps the cell, the bees remove the dead larva

14. This experiment on hygienic behaviour of honey bees clearly shows the influence and control of two genes on the hygienic behaviour of honey bees. Many other behaviour patterns studied in various animals are found to be polygenic. The courtship song of cricket is under the control of many genes. All courtship displays, nest building, parental behaviours, bird songs are also controlled by many genes. Hybrids of two species of Swordtail fish ( Xipophorus helleri and E montezumae ) show that even simple behavioural difference in courtship behaviour can be polygenic. Digler (1990) proposed that nest building behaviour in animals is polygenic.

15. Conclusion T here is no such thing as a gene for any behaviour pattern. There is no aggression gene, no gay gene, no gene for bird song or nut-burying. Genes encode  proteins, nothing more; but through proteins, they can influence behaviour. Evolution has acted so that benefit from generations of natural selection on behaviour. Learning gives animals tools to respond to local conditions and changing environments. Behaviour is best seen as the result of evolutionary processes that sometimes create, through genetic coding, behavioural instructions for animals and at other times create flexible mechanisms to allow animals to solve problems specific to their environment .