Selfish genetic elements such as selfish chromosomes increase their transmission rate relative to the
rest of the genome and can generate substantial cost to the organisms that carry them. Such
segregation distorters are predicted to either reach fixation potentially causing population
extinction, or more commonly, promote the ...
Selfish genetic elements such as selfish chromosomes increase their transmission rate relative to the
rest of the genome and can generate substantial cost to the organisms that carry them. Such
segregation distorters are predicted to either reach fixation potentially causing population
extinction, or more commonly, promote the evolution of genetic suppression to restore
transmission to equality. Many populations show rapid spread of segregation distorters, followed by
the rapid evolution of suppression. However, not all drivers display such flux, instead persisting at
stable frequencies in natural populations for decades, perhaps hundreds of thousands of years, with no
sign of suppression evolving or the driver spreading to fixation. This represents a major evolutionary
paradox. How can drivers be maintained long-term at stable frequencies? And why has suppression not
evolved as is the case in many other gene drive systems? Here we explore potential factors that may
explain the persistence of drive systems, focusing on the ancient sex-ratio SR driver in the fly Drosophila
pseudoobscura. We discuss potential solutions to the evolutionary mystery of why suppression does not
appear to have evolved in this system, and address how long-term stable frequencies of gene-drive can
be maintained. Finally, we speculate whether ancient drivers may be functionally and evolutionarily
distinct to young drive systems.