The Drosophila fruit fly revolutionized the study of genetics early in the twentieth century when it allowed biologists to conduct multi-generation experiments into heredity and genetic change. At the same time, however, it is important to bear in mind not only the similarities between DNA in all life (including the human genome and Drosophila fruit flies), but the significant differences as well.
Fruit flies are a favourite of biologists mainly because of their life cycle. It is easy and cheap to breed fruit flies – indeed, in the wild most of them breed precisely where they’re not wanted, such as spoiled fruit in household kitchens. The hatchlings mature into fertile adults in mere days, and their entire lifespan is only a month or less. This means that biologists can rapidly breed multiple generations of fruit flies in the space of a year, and can trace in months or years multi-generational changes that would only be seen in larger mammals, like primates (and, ultimately, human beings) only in thousands of years. In human-equivalent years, over the past century we have monitored tens of millions of years of evolution in captive fruit flies. Ultimately all DNA operates according to similar principles, which is why we can extrapolate from studies on small fruit flies to make theories about the evolution of much more sophisticated life forms.
At the same time, there are significant differences between the human genome and fruit fly genomes. The most important of these is size. The fruit fly genome consists of about 165 million genetic base-pairs spread along four chromosomes. In contrast, the human genome consists of several billion base-pairs, on 23 different chromosomes. (Chromosomes are paired from the mother and father, resulting, for example, in a full genetic code of 46 chromosomes in each individual human being.)
In the same way, another often-hyped “similarity” – that we share a large amount of our genes with fruit flies – actually points to another, more significant difference. A large number of genes is shared by virtually all species of animals. In addition to fruit flies, about one-third of the genome of the C. elegans roundworm is also shared with humans – and we share over 95% of our genome with close relatives like the chimpanzee. This has led to claims that, for instance, we share half our DNA with bananas and 60% with fruit flies. In the case of comparisons with simpler animals like fruit flies, though, these comparisons are highly misleading. As the Wellcome Trust observes, all of the “common” DNA is crammed into the comparatively small fruit fly DNA code, which is far shorter than the human genome.