Whole Genome Assemblies for Two Southern African Dwarf Chameleons

 

    In the genomics world, a database of expansive and comprehensive data for species' genomes is essential to understand evolution of the species and their characteristics. Researchers previously did not have comprehensive data on the Bradypodion genus and African taxa due to lack of resources, leaving many questions. Recently, the southern African dwarf chameleon has been the primary area of interest. Although initially thought to have convergent evolutionary traits, it has been identified they have a high amount of synteny. Most surprisingly, despite the Anolis genus diverging from this lineage 170 million years ago, synteny is still maintained among these species. C. calyptratus differs from this chameleon genus as sex is determined by XX & XY chromosomes. At some point divergence must have occurred and the ZZ/ZW sex chromosomes must have evolved. Although Bradypodion has not been known to possess the X chromosome, it is hypothesized that sex determination must reside in a different chromosomal location. Researchers were able to identify that these species were the most contiguous reptiles found as of current.  As research develops, tracking the lineages and understanding evolutionary trait development is important in understanding the origin and adaptation abilities of these intriguing reptiles.

Reptile Database- Bradypodion

De Novo Whole Genome Assemblies for Two Southern African Dwarf Chameleons (Bradypodion, Chamaeleonidae)

Odorrana Swinhoana Provides Clues on the Evolution of XY Systems

    Odorrana swinhoana is a frog species that has six sex chromosomes. This is rare in amphibians; scientists have only discovered multiple sex chromosome systems in 10 species of amphibian. "The O. swinhoana frog species is the first vertebrate known to retain descendant genes that now determine sex in mammals, birds, and fishes inherited from a common ancestor" (Hiroshima University).
    

    Translocations are chromosomal abnormalities that happens when a chromosome breaks and its fragment fuses to another. The first discovered case of this occurred in 1980, with the Raina narina. Their sex chromosomes are X1Y1X2Y2 for males and X1X1X2X2 for females. The sex chromosomes for O. swinhoana for males and females are X1Y1X2Y2X3Y3 and X1X1X2X2X3X3 respectively; three translocations in males created this system of six sex chromosomes.

    The male determining gene in birds, Dmrt1, and in platypus and fish, Amh, are located on the Y1 chromosome of male O. swinhoana. Also, the therian mammals' ancestral SRY gene, Sox3, is located on the Y3 chromosome. The major sex-determining gene out of the three aforementioned ones isn't known yet. However, the discovery of these genes gives some information on the relationship between these animals. They may share a common DNA sequence.
    Their data suggests that these translocation are nonrandom. It gave them a new viewpoint on the evolution of multiple sex chromosome systems.



https://www.sciencedaily.com/releases/2021/04/210413081357.htm

https://www.technologynetworks.com/genomics/news/taiwanese-frog-species-found-to-have-six-sex-chromosomes-347609

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.

Evolution of Chromosome 2 in White-Throated Sparrows May Give Clues to Evolution of Sex Chromosomes

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.

http://www.nature.com/news/the-sparrow-with-four-sexes-1.21018

https://www.sciencedaily.com/releases/2014/01/140114203121.htm