Highly dynamic intercourse chromosomes in cichlid fishes

The cichlids of Lake Tanganyika in Africa are extremely various—together with with regard to intercourse chromosomes. These have modified extraordinarily regularly in the middle of the evolution of those fish and, relying on the species, might be of the sort XY or ZW. This has been reported by a analysis crew from the University of Basel and the Research Museum Koenig in Bonn within the scientific journal Science Advances.

Based on the biology classes again in our schooldays, we all know that XX means feminine, and XY means male. In mammals, these constellations of intercourse chromosomes decide whether or not a person turns into a feminine or a male. It is totally different in birds, the place the precept of ZW = feminine, ZZ = male applies. In many reptiles, the temperature at which the eggs develop determines the intercourse. The method by which genetic intercourse is decided can due to this fact range from species to species, with totally different sex-determining methods having occurred throughout evolution. In fish, probably the most biodiverse group of vertebrates, we discover totally different genetic methods (together with the XY and ZW varieties of mammals and birds, respectively) in addition to environmental methods (as in lots of reptiles).

The evolution of intercourse chromosomes

Sex chromosomes are derived from “normal” chromosomes—the autosomes—after buying a brand new, sex-determining mutation. The ensuing new chromosome pair takes separate paths in the middle of evolution, guaranteeing that there isn’t a trade of sex-determining genes between the 2 intercourse chromosomes.

In mammals, this course of passed off round 165 million years in the past, and resulted within the XY system with a male-specific Y chromosome. In birds, the W is a female-specific chromosome. In fish, however, it has been recognized for a while that there isn’t a common intercourse chromosome system.

With the help of next-generation genome sequencing strategies that enable for a comparability between the genomes of each sexes, a brand new world of intercourse chromosomes has been recognized in fish: During their evolution, totally different chromosomes have developed independently of one another in several fish lineages as intercourse chromosomes. Yet, the repeated look of comparable or functionally associated sex-determining genes suggests that there’s a pool of chromosome candidates which can be notably appropriate for intercourse willpower.

Cichlids are particularly various

A analysis crew on the Department of Environmental Sciences on the University of Basel led by Dr. Astrid Böhne (now on the Research Museum Koenig in Bonn) has now investigated the evolution of intercourse chromosomes in a extremely various group of fish, the cichlids from Lake Tanganyika in Africa. A specific function of those fish is that they’re a chief instance of adaptive radiation, a course of by which numerous species emerge in a comparatively brief time via speedy adaptation to varied habitats.

The researchers analyzed intensive genome and transcriptome information of round 240 cichlid species for variations between females and males, which enabled them to determine intercourse chromosomes in over 70 species. Interestingly, substantial variations between the species turned obvious with regard to the chromosomes accountable for intercourse willpower. The course of the evolution of cichlids in Lake Tanganyika additionally noticed a number of modifications from sex chromosomes of sort XY to ZW and vice versa.