It is na ve to try to break down behaviors into strictly nature vs nurture categories Human height is an example of an anatomical outcome that is the result of both genetic factors and the environment Predominantly Environmental Interactional Predominantly Genetic Specific language Height Blood type Specific religion Weight Eye color Skin color It is also na ve to divide behaviors into innate like a FAP or learned Another cool behavior website This one is from Dr Kent Simmons at the University of Winnipeg There are many opportunities for the environment to influence behaviors see Figure 5 1 in Text However what behavioral geneticists try to do is tease apart the influences of genetics and the environment because the evolution of behaviors or any characteristic does not proceed unless there is at least a partial genetic basis Once in a while we get lucky and can clearly see the behavioral results of a single or small set of genes This is the case when we compare 2 strains of honeybees Apis mellifera hygienic and unhygienic American foulbrood is a bacterial disease that can infect larvae Most strains of honeybees are hygienic meaning that if the workers detect that a bee larva has been infected by the bacillus Paenibacillus larvae they will uncap the cell and remove the diseased larva A Mendelian cross can be done between true breeding homozygous hygienic bees and unhygienic bees When this is done the F1 generation of heterozygotes are all unhygienic Thus the hygienic allele s is are recessive or unexpressed And then a F1 X F1 cross is performed When a F1 X F1 testcross is performed on the bees the following behaviors result 1 Uncap cells but do not remove larva 2 Remove dead larva from previously uncapped cells 3 Not uncap or remove larva 4 Uncap cells and remove larva This tells us that there are at least 2 and possibly more genes responsible for the behavior of 1 uncapping the cell and 2 removing the dead larva Honey bee larvae infected with American foulbrood become a stringy mass of material that later dries and carries the spores that may infect other larvae So the bees are showing all the evidence of a dihybrid testcross Mutations and Knockout genes have provided some insight into the relationship between genes and behavior When mutations are deliberately caused using a mutagenizing technique such as chemicals or x rays there is no control over the site or extent of the damage or alteration of the DNA This technique usually leads to animals that are sick or dysfunctional and because the mutations are random in nature it is time consuming and expensive Knockout gene studies on the other hand are a more fine tuned approach In a knockout procedure a specific gene is targeted and disrupted Then the resulting animals are screened to find out which have the knockout gene in their DNA These animals are bred to create a strain of animals that are homozygous for the inactivated gene The resulting animals are studied for any behavioral changes that might occur as a result of the inactivated gene These techniques have already yielded examples of mutations at single gene loci that result in major disruptions of normal behavior Paramecium Drosophila Sluggish Spinner Paranoiac Spinster Dunce Rutabaga Amnesiac Fruitless As evocative as these studies are remember that these genes might also be important in developmental processes or in the normal functioning of the central nervous system So further research is focusing on exactly which systems are disrupted by a given mutant Remember too that pleiotropy a single gene having multiple phenotypic effects and epistasis the action of one gene affecting the action of one or more other genes can complicate what might seem to be a relatively simple gene behavior relationship fosB mutant information Other techniques have been used to examine putative single gene effects e g mosaics but most behavioral traits are caused by multiple gene polygenic effects These include some intuitively simple experiments such as cross fostering These pictures actually shows adoption not cross fostering and are part of an urban legend Click on right picture to read about the myth Great Egret chicks regularly commit siblicide Great Blue Heron chicks rarely do Mock 1984 hypothesized that the small bits of food given by Great Egret parents to their chicks enabled aggressive chicks to monopolize the food and kill their nestmates So he did a cross fostering experiment Great Egret chicks regularly commit siblicide Great Blue Heron chicks rarely do The result was that Great Blue Heron chicks given small bits of food by the Egret parents became siblicidal indicating that the environment can induce siblicide in the Blue Heron species In contrast Egret chicks remain aggressive even when given the large pieces of food typical of Blue Heron parents Other ways to look at multiple gene effects in an intuitive manner are twin and adoption studies Most behavioral traits are polygenic so if you measure and graph them it will result in a normal or Gaussian distribution Another way to examine multigenic traits is by quantifying the amount of variance in a population due to genes versus that due to the environment VP VG VE Variance of phenotype Variance of genotype Variance of environment Multigenic effects Quantitative Studies We can measure genetic transmission of traits through heritability analyses In behavioral and population genetics there are 2 basic types of heritability 1 broad sense 2 narrow sense Heritability of 0 Heritability of 1 0 Usually the heritability of a characteristic including behavioral is somewhere between 0 and 1 0 In Broad Sense Heritability the question is What proportion of the variance in a trait is attributable to genetic variance Broad Sense Heritability measures the total proportion of variance in a trait that is genetic variance as opposed to environmental variance Example 1 Raise mice in identical environments and measure their foraging behavior 2 Differences in behavior should be due to genetic differences among individuals genetic variance or G 3 Raise mice in dramatically different environments 4 Now differences are due to G E E environmental variation To measure the Broad Sense heritability H G G E where H Heritability G Genetic variance E Environmental variance G E phenotypic variance Example Human Intelligence In Narrow Sense Heritability the question is What portion of genetic variance is accessible to natural selection It can be used to predict