14 DAY TRIAL // Males change faster than females. Just look at a peacock's tail feathers compared to the plain peahen. In most species, males are brighter and better singers, competing for getting as much as possible mates. This way they experience sexual selection. This overdrive compared to females puzzle the scientists, as they share the same genes with the females.
In a new research published in the Proceedings of the National Academy of Sciences, a team at the University of Florida Genetics Institute tries to give an answer.
"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.
The team investigated gene expression in male and female fruit flies employing microarray analysis, which can observe the activity of thousands of genes at the same time. The sole genetic difference between the flies was that females possessed two X chromosomes and males one X and one Y chromosome. The extra X in females seems to explain the slow selection in females.
Females have two versions of X-linked genes that not only interact one with each other, but also with other genes from the other chromosomes. As males have just one version of the X chromosome, there are less interactions of X genes, while the Y chromosome comprises 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.
Because of the simpler genetic pathway, males react quickly to the pressures of sexual selection. "This research shows how recessive and dominant traits are important in determining variation in populations. The best way to think of it is males play with one card, but females get to play one and hold one. If males have got a good trait, it's promoted; something bad, it's eliminated. In females you can have a bad card, but a good card can protect it. As a result, females can carry deleterious traits but not express them.", said David Rand, a professor of biology at Brown University, not involved in the study.
8,607 genes common in both sexes were analyzed, of which 7,617 expressed differently, thus the same genes work differently in males and females. We have over 65 % of DNA common with the fruit fly, including genes involved in some cancers, Alzheimer's disease and heart disease. This research also shed light on why men and women react differently to the same disease. "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.", Wayne added.