Sunday, November 27, 2016

The sparrow with four sexes

A scientific team consisting of husband and wife ornithologists has gathered years of research about the white-throated sparrow, Zonotrichia albicollis. The bird has a tan morph and a white morph, where there are males and females with white stripes on their head and males and females with tan stripes on their head. This difference in coloration is caused by a genetic mutation in Chromosome 2. Somehow, the chromosome was inverted so a large section of genetic information could not link up with a partner chromosome in reproduction. This led to the formation of a "supergene", allowing the chromosome and its information to evolve like how a sex chromosome would.

Over time, it was discovered that the sparrow acted as if it had four sexes instead of two. The difference in chromosomes allowed the birds to evolve into the different morphs with their own characteristic physical attributes and behaviors. The tan-striped birds are monogamous and overprotective of their offspring, while the white-striped birds are promiscuous and poor parents. The sparrow morphs do not mate with each other; tan-striped birds do not mate with tan-striped birds. Instead, in what is called disassortive mating, tan-striped birds almost always mate with white-striped birds, creating a further divide and establishment in the evolution of the four sexes.

This development in research allows so many different questions to be pursued. The role of genes in behavior can be investigated; the ability of an autosome to mutate and evolve like it is a separate sex chromosome can be analyzed; and finally, we can see if the formation of "supergenes" could possibly be used to benefit us or other organisms somehow.


  1. This is really interesting, I have not heard of the formation of a supergene prior to this. It is strange that the genetic information in the chromosome was unable to link with the partner chromosome when reproducing. It is also interesting that the different morphs display different behaviors. It would be interesting to see if this case has happened in any other types of species and what kind of behaviors they display, if similar to this.

  2. It is interesting how the sexes are determined by behavior rather than physiological aspects of the bird. The different behaviors will cause a great change in which birds are dominant in the population. For example, while the the tan sparrow are protective of their young the white striped birds are more sexually active and reproduce more often as a result. This would most likely lead to a greater number of white stripe sparrow to the tan sparrows.

  3. I have never heard of a supergene before this, but many aspects of this are so interesting. The fact that sex is determined by behavior and that the chromosome information was unable to link with the partner chromosome when reproducing is so strange. It would be interesting to see how many more species have interesting occurrences like this.