credit: university of sheffieldthe size and swimming speed of sperm are controlled by a single supergene in birds, according to a new study by the university of sheffield. sperm competition is an important selective force in many organisms but the relationship between sperm shape, its ability to move and successful fertilisation is only partly understood.previous studies have shown that sperm shape and speed are inherited; fathers with long, fast sperm have sons with long, fast sperm. however, it was not known which genes were responsible for sperm characteristics being passed from one generation to the next.in a new study, published today in nature ecology and evolution, researchers at the university of sheffield have used zebra finches as a model system to unravel the genetics of sperm.the new research shows that the shape, size and swimming speed of sperm is due to something called a supergene. a supergene is a number of genes that are next to each other on a chromosome and inherited together as one unit. the idea that supergenes were important was first proposed in the 1930s, but evidence for them was lacking until recently.professor jon slate, from the department of animal and plant sciences at the university of sheffield, said: `like humans, birds have sex chromosomes; males have two z chromosomes and females have a z and a w. the zebra finch supergene that affects s...