Courtship

Previews studies have shown that genes control a myriad of behaviors.  Even complex behaviors such as learning are controlled by genes.  It was not a surprise when scientists found a gene which controls courtship behavior.  Courtship display is a special, sometimes ritualized, set of behaviors which some animals perform as part of courtship.  Courtship behaviors can include special calls, postures, and movements, and may involve special plumage, bright colors, or other ornamentation.  Courtship is a vital behavior that facilitates a species’ ability to procreate and pass along its genes to the next generation.  A mutation in the gene that controls the courtship behavior, would greatly affect the animal’s courtship behavior and endanger the species’ survival in the world. 

Fruit flies have been used as a primary animal model for the study of the genetics behind courtship display due to its very distinct nature.  First, the male fly orients itself towards the female fly.  Next, the male fly starts tapping its foreleg on the female fly and  vibrating its wing (which is perceived as singing) to the female fly.  Last, the male fly licks the female fly and then attempts copulation.   (See figure below)

However, when a specific gene is mutated, the fruit flies’ courtship display content and their targets change.  Scientists named this courtship controlling gene fruitless, fru.  There are two forms of proteins from the fru gene - fru^M, which is only produced in the male fly, and fru^F, which is only produced in the female fly.  A series of experiments demonstrated the importance of these genes in courtship behavior.  When fru^M is replaced by fru^F, the male fly displays its courtship behavior towards a male instead of a female.  These fru^F–expressing male fly also display an bizarre and unnatural behavior called chaining during which all mutated male fly follow each other in a line.  (See video).  Scientists also found that when fru^M is expressed in the female fly, the female fly displays male courtship behavior towards another female fly.  (Stockinger, et at., 2005)  Reasons for these mutated flies to display lose differentiation between sexes are still unknown.  The effect of the fruitless gene on the fruit fly’s courtship behavior, however, is conspicuous.

Human courtship behaviors are more complex and less distinct.  Therefore, pinpointing a gene that changes our behaviors is far more difficult.  Nonetheless, a molecular geneticist of the National Cancer Institute, Dean Hamer, caused a great stir in the scientific community.  In 1993, he discovered a certain region (which Hamer named Xq28) on one of the X chromosomes (that is, the chromosomes passed from a mother to a son) was 82% similar to brothers who were both identified as homosexual.  However, no conclusion has been drawn from this study because no one has been able to duplicate Hamer’s study.  Furthermore, a similar experiment that was conducted by George Ebers (a neurogenetecist in the University of Western Ontario), showed that the Xq28 region was not consistently shared by homosexual brothers, contradicting Hamer study.

Nature versus nurture theories have long been debated.  Most would agree that our behaviors, possibly including courtship behavior and sexual orientation, are likely a product of both innate character (i.e. our genetic makeup) as well as influences of our environment.  Continued research on the relationship between genes and behavior will further our understanding of the essence of what makes us who we are.