Genome of South African dwarf chameleons decoded

Genome of South African dwarf chameleons decoded

by Alex Negro Science

After a reference genome for the panther chameleon (Furcifer pardalis) was recently published for the first time in China, scientists from South Africa have now followed with the genome of two dwarf chameleon species.

For the analyses, a male Bradypodion pumilum from Cape Town and a male Bradypodion ventrale from an introduced population in Johannesburg were taken. Muscle and liver tissue was used for long sequencing (HiC). The genome size of Bradypodion pumilum is 2.43 gigabase pairs (Gb), that of Bradypodion ventrale 2.40 Gb. The BUSCO analysis demonstrated a high completeness with about 97% of all existing coding genes in vertebrates. Furthermore, the current publication confirms the six macrochromosomes already found from the karyotype in Bradypodion thamnobates 2017. Various comparisons with Anolis sagrei were made. It remains open which chromosomes in Bradypodion are sex chromosomes.

The genomes can be viewed in the NCBI BioProject under the number PRJNA9861319 and under the BioSample numbers SAMN35825189 and SAMN35825190 respectively.

De novo whole genome assemblies for two Southern African Dwarf Chameleons (Bradypodion, Chamaeleonidae)
Jody M. Taft, Krystal A. Tolley, Graham J. Alexander, Anthony J. Geneva
Genome Biology and Evolution 15 (10), 2023, pp. 1-8
DOI: 10.1093/gbe/evad182

Karyotypes in chameleons

Karyotypes in chameleons

by Alex Negro Science

Scientists from Great Britain and Italy have now studied the chromosomes of different chameleon species. They examined the karyotype of a total of 83 different chameleon species. Among them were 57 Madagascan chameleon species, of which 32 karyotypes were described for the first time ever. For Calumma brevicorne, Calumma fallax, Calumma parsonii and Furcifer verrucosus, there were even several animals each available for examination. The scientists found out that presumably the fusion of chromosomes has reduced the total number of chromosomes in the course of evolution in chameleons. Presumably, it was mainly microchromosomes (particularly small chromosomes) that fused.

Microchromosome fusions underpin convergent evolution of chameleon karyotypes
Marcello Mezzasalma, Jeffrey W Streicher, Fabio M Guarino, Marc E H Jones, Simon P Loader, Gaetano Odierna, Natalie Cooper
Evolution, Juni 2023
DOI: 10.1093/evolut/qpad097

 

Genetics: Karyotype in the Veiled Chameleon

Genetics: Karyotype in the Veiled Chameleon

by Alex Negro Science

It has been known for some time that the sex of the Veiled chameleon (Chamaeleo calyptratus) is genetically determined. The species has an XX/XY system. Scientists from Russia, Great Britain, Italy, and Thailand have now studied the karyotype of the species, i.e. the characteristics of the chromosomes.

The probably most original karyotype of all chameleons is 2n= 36. This “primal chameleon” had six pairs of metacentric macrochromosomes and twelve pairs of microchromosomes, particularly small chromosomes. The Veiled chameleon, on the other hand, has a smaller number of chromosomes, namely only 2n=24. Using various genetic investigation methods, the researchers in the present study found that this karyotype probably arose through fusions. Microchromosomes apparently fused with each other twice, and micro- and macrochromosomes fused no less than four times. The latter, the so-called heterogeneous fusion between chromosomes of different sizes, is unusual for vertebrates. Normally, macro- and microchromosomes are located at different locations in the cell nucleus and are transcribed and replicated at different rates. However, this phenomenon is already known from alligators and turtles – for chameleons it is new.

Until now, it was also unclear which pair of chromosomes in the Veiled chameleon is actually responsible for the sex. In Chamaeleo chamaeleon, the second largest chromosome pair codes for sex. However, initial speculation suggests that in the Veiled chameleon the fifth chromosome pair (CCA5) may instead be the sex chromosome pair. The conjecture still needs to be validated by further research. It is also still up for discussion which gene is actually predominantly responsible for the development of the sex organs in the embryo – the researchers identified at least three possible genes on CCA5.

Identification of Iguania ancestral syntenic blocks and putative sex chromosomes in the Veiled Chameleon (Chamaeleo calyptratus, Chamaeleonidae, Iguania)
Katerina V. Tishakova, Dmitry Yu. Prokopov, Guzel I. Davletshina, Alexander V. Rumyantsev, Patricia C. M. O’Brien, Malcolm A. Ferguson-Smith, Massimo Giovannotti, Artem P. Lisachov, Vladimir A. Trifonov
International Journal of Molecular Sciences 23, December 2022
DOI: 10.3390/ijms232415838