The observation that males evolve more quickly than females has been in existence ever since 19th century biologist Charles Darwin pointed out the majesty of a peacock's tail feather in comparison with the plainness of the peahen's.
Males are known to have flashier features and more melodious warbles in an eternal competition to win the best mates, a concept known as sexual selection. But it has been a mystery why males are in evolutionary overdrive, even though they have essentially the same genes as females.
Now, the new study appearing online in the Proceedings of the National Academy of Sciences sheds some light on the issue. "It's because males are simpler. The mode of inheritance in males involves simpler genetic architecture that does not include as many interactions between genes as could be involved in female inheritance," said Marta Wayne, an associate professor of zoology in the College of Liberal Arts and Sciences and director of UF's Graduate Program in Genetics and Genomics.
During the study, the research team examined how gene expression is inherited differently in male and female fruit flies using microarray analysis, which is a way to monitor the activity of thousands of genes simultaneously. The flies were identical genetically, except that females have two X chromosomes and males have a single X and a single Y chromosome.
The study suggested that extra X chromosome in females might make answering the call of selection more complicated. According to the researchers, sex cells from a mother and a father combine to make an embryo in flies or humans. Females are equipped with two versions of X-linked genes that interact not only with each other, but also with other genes. Whereas, males have only one version of the X chromosome, making for fewer interactions and more straightforward male inheritance, especially since the male's Y chromosome contains very few genes.
"In females, a dominant allele can hide the presence of a recessive allele. In contrast to females, which have two X chromosomes, one inherited from each parent, males have only one X inherited only from their mother. This is a simple mechanism that could be working in cooperation with sexual selection to help males evolve more quickly," said Lauren McIntyre, an associate professor of molecular genetics and microbiology in UF's College of Medicine.
The researchers believe that the relatively uncomplicated genetic pathway helps males respond to the pressures of sexual selection, thereby enabling them to win females and produce greater numbers of offspring.
The scientists analysed 8,607 genes that are shared by both sexes of a fruit fly called Drosophila melanogaster. They found that 7,617 of the genes were expressed differently in males and females, indicating that the same genes do different things.
The researchers believe that their finding may lead to the advancement of understanding as to why diseases may present themselves or respond to treatment differently in men and women. "There's a health aspect in figuring out differences in gene expression between the sexes. To make a male or a female, even in a fly, it's all about turning things on -- either in different places or different amounts or at different times -- because we all basically have the same starting set of genes," said Wayne.