White-throated sparrows are an incredibly
interesting and unique species due to the evolution of chromosome 2. A mutation caused a section of this chromosome, containing more than 1,100 genes, to flip.
This resulted in two different “supergenes” that are unable to undergo
recombination, and therefore created two different morphs. While the
white-striped morph is aggressive, promiscuous, and sings very well, the
tan-striped morph is protective, monogamous, and sings poorly. However, each
morph only mates with the other morph, and same-morph matings are extremely
rare. Because of the mating selection and lack of recombination between
chromosomes, scientists believe they are witnessing the evolution of another set
of sex chromosomes.
Through genetic analysis, scientists Rusty
Gonser and Elaine Tuttle discovered that chromosome 2 contains a series of
inversions rather than a single large one. The white morphs contain the
inverted chromosome, while the tan morphs do not. Many of the inverted genes code
for physical and behavioral differences, including the estrogen receptor alpha (ER-alpha), which dictates behavior. They also discovered that the inverted
part of the chromosome was undergoing mutations much faster than other
chromosomes, mirroring the rapid mutation rate of the evolution of sex
chromosomes. However, because of the limit on viable mates due to only being
able to mate with ¼ of the population instead of ½, scientists believe that
this is not an evolutionary advantage, as it would require much more effort for
individuals to find a mate. This may explain why most vertebrates only have two
sexes.
This experiment is imperative to
biologists so that we can learn more about how sex chromosomes evolved, and
subsequently apply this method to other species. It challenges scientists to
think outside the box about what we already know so that we can use our
knowledge and apply it on a broader scale. It may also improve research efforts
in researching other species that may have been overlooked as potentially
having a second pair of sex chromosomes.
No comments:
Post a Comment