Evolution is quite complicated. Each species has been transformed over hundreds of thousands of years to become what it is today.
This process is practically imperceptible due to how slowly it happens and the minimal magnitude of the changes that take place, but many species have similarities that relate them to each other, and most families of animals keep their similarities not only in their physical appearance but also in their genetics.
More than 50 years ago, evolutionary biologist Susumu Ohno discovered peculiar patterns in the genes of a mammal. Creeping voles, like the rest of mammals, have chromosomes that determine their sex.
But unlike what would be normal, female creeping voles only have one X chromosome in their genes and a double X is found in the sex chromosomes, when in the rest of mammals our sex cells halve their chromosome numbers, inside the tissues that produce ova.
Males are more like the rest of the species, they have two chromosomes throughout the body, X and Y, and only one Y chromosome is found in the sex genes, always the same chromosome to the surprise of scientists. Or so they thought.
Scientists have not been able to understand the origin of this genetic difference and when evaluating related and close animals in the evolutionary line they realize that other voles do not have this same characteristic so they affirm that this genetic mutation must have occurred in creeping voles less than two million years ago.
“This is basically the weirdest sex chromosome system known to science,” said biologist Scott Roy who, together with a team of scientists, embarked on a mission to try to understand this mystery.
The research resulted in scientists discovering that what had previously been labeled a Y chromosome is actually a remnant of another X chromosome and some sequences of Y, which are ultimately what determines the sex difference at birth.
The research is impressive, and scientists still cannot understand the depth of the mystery and why this species does not have Y chromosomes and still manages to reproduce with differentiated sexes.