## Lazy and drunk flies

Fruit flies, Drosophila melanogaster, which are one of the most frequently used model organisms in genetics, does not bypass behavioural genetics either. Some regions of human genes that have been associated with various neurobiological disorders have related genes present in the genome of these flies. Therefore, Drosophila have become a valuable tool for the analysis of various diseases and disorders. An example is a mutation in the gene for the protein kinase G enzyme, which is believed to be related to the increasingly common neurodevelopmental disorder of attention associated with hyperactivity, known as ADHD (attention deficit hyperactivity disorder). The protein kinase G enzyme is encoded by the DG2 gene in fruit flies. Depending on the specific type of allele located at the respective locus, different production levels of the protein occurs, which subsequently affects the behaviour of flies in search of food. Individuals with rover alleles are able to cover greater distances in search of food than individuals with a phenotype conditioned by sitter alleles (Figure 13.2). Although this pattern of behaviour is conditioned by an allele of one gene, as in many other cases, there is an interaction with other genes and a polygenically conditioned phenotype.

An interesting example of genetically determined behaviour is the relationship of male fruit flies to alcohol. This relationship is influenced by courtship, which consists of dancing, singing or even gentle touches on the females. If the male's efforts fail, he loses interest in females and compensates for the failure with increased alcohol intake. This is due to low levels of NPF, which is a neuropeptide also found in the human brain. A decrease in the level of NPF can also occur in females, in which it also causes an increased preference for ethanol. The reason is not a loss of interest in mating, but a reaction to the appearance of a parasitic wasp in the environment. In its presence, female flies begin to prefer laying eggs on alcohol substrates, thereby providing the future larvae with the necessary protection against wasp infection. Exposure to such predators can thus lead to epigenetic changes, which you learned more about in Chapter 7 - From epigenetics to diseases. The epigenetic state causing reduced NPF formation, can be inherited in up to five generations. Such studies provide valuable information that can be used in the investigation of hereditary preference for drug or alcohol use.

The researchers also identified several different mutations in genes related to alcohol consumption. The hangover mutation is associated with low tolerance to alcohol. Flies with this mutation do not need to increase doses to achieve the same effect as standard flies without the mutation, so they are less likely to become addicted. It is the same with the krasavietz mutation, which leads to decreased tolerance and taste for alcohol. Flies with this mutation do not show pleasure nor stimulating effects after consuming alcohol. The happyhour mutation has the opposite effect, which manifests itself in low sensitivity to alcohol, and the mutant flies thus experience pleasant feelings after consuming it.