Navigation Links
East African cichlid fish offer new understanding of genetic basis of sex determination

Biologists have genetically mapped the sex chromosomes of several species of cichlid fish from Lake Malawi, East Africa, and identified a mechanism by which new sex chromosomes may evolve.

In research published in this week's issue of the journal Science, biologists Thomas Kocher, Reade Roberts and Jennifer Ser of the University of Maryland describe the genetic basis for two co-existing systems of sexual determination in cichlid fish from Lake Malawi.

"This study marries two evolutionary mysteries: the incredible diversity of fish in the lakes of East Africa and the genetic basis of sex determination," says Sam Scheiner, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research. "Simple genetic changes can lead to enormous biological diversity."

In nearly all mammals, the SRY gene determines the sex of offspring and is located on the Y chromosome, which is much smaller than the X chromosome.

But in many other animal groups, the genetic mechanism of sex determination evolves quite rapidly, and the differences between sex chromosomes are harder to observe.

Even sister species of fish may have entirely different sex determination systems. How and why the genetic mechanisms for such an ancient developmental distinction continue to evolve has remained a mystery.

The thousands of closely related cichlid fishes in the lakes of East Africa turn out to be an excellent model system for understanding how the mechanisms of sex determination evolve.

The East African cichlid fishes that inhabit Lakes Malawi, Tanganyika, and Victoria are known for their sexually distinct appearance--the males are generally conspicuous and brightly colored, making them more attractive to females, while the females are drab and brown, making them inconspicuous to predators.

One exception to the uniformly brown pigmentation among female cichlids is the "orange blotch" pattern, which appears in some female cichlids that live in rocky areas of Lake Malawi.

"We believe that the orange blotch color pattern emerged as a new mutation in females and has a selective advantage in providing an alternative form of camouflage," says Kocher.

Depending on the surrounding natural background, this color pattern can help disguise female fish and help them avoid predation.

However males who express this phenotype lack the species-specific color patterns used by females to select their mates.

"This phenotype creates a sexual conflict because the allele is favored in females but not favored in males," explains Roberts, who mapped the gene. "In 'survival of the fittest,' the genes underlying a beneficial trait will increase in frequency, but this is an odd case where the trait is really good for females but really bad for males."

Using genomic techniques, Roberts identified the gene (pax7) that is responsible for this difference in color pattern.

He found that the orange blotch (OB) allele that produces the variable pigmentation in females was dominant over the "brown barred" (BB) allele (that produces the more common brown pigmentation) and that it was located very near a female sex determiner.

The genetic conflict that started over color was resolved by a new mutation that took over the sex-determining function, and ensured that nearly all orange blotch fish are female.


Contact: Cheryl Dybas
National Science Foundation

Related biology news :

1. Google Earth aids discovery of early African mammal fossils
2. Going bananas for sustainable research -- scientists create fuel from African crop waste
3. Difference in fat storage may explain lower rate of liver disease in African-Americans
4. Cleaning the atmosphere of carbon: African forests out of balance
5. Ancestral genome of present-day African great apes & humans had burst of DNA sequence duplication
6. African-Americans aware and accepting, but often do not receive, the HPV vaccine
7. Nutritional supplementation program helps prevent weight loss among children in African country
8. African thicket rat malaria linked to virulent human form
9. Ancient African exodus mostly involved men, geneticists find
10. Ecological impact of African cities
11. Hypertension develops early, silently, in African-American men
Post Your Comments:
(Date:10/29/2015)... 29, 2015   MedNet Solutions , an innovative ... of clinical research, is pleased to announce that it ... (MHTA) as one of only three finalists for a ... Small and Growing" category. The Tekne Awards honor ... superior technology innovation and leadership. iMedNet™ ...
(Date:10/29/2015)... , Oct. 29, 2015  Rubicon Genomics, ... for U.S. distribution of its DNA library preparation ... and Rubicon,s new ThruPLEX Plasma-seq kit. ThruPLEX Plasma-seq ... the preparation of NGS libraries for liquid biopsies--the ... diagnostic and prognostic applications in cancer and other ...
(Date:10/29/2015)... , Oct. 29, 2015 Today, ... announced a partnership with 2XU, a global leader ... deliver a smart hat with advanced bio-sensing technology. ... other athletes to monitor key biometrics to improve ... strategic partnership, the two companies will bring together the ...
Breaking Biology News(10 mins):
(Date:11/25/2015)... Nov. 25, 2015  PharmAthene, Inc. (NYSE MKT: PIP) ... a stockholder rights plan (Rights Plan) in an effort ... carryforwards (NOLs) under Section 382 of the Internal Revenue ... PharmAthene,s use of its NOLs could be substantially ... defined in Section 382 of the Code. In general, ...
(Date:11/25/2015)... and HOLLISTON, Mass. , Nov. ... (Nasdaq: HART ), a biotechnology company developing bioengineered ... Jim McGorry will present at the LD ... 2015 at 2:30 p.m. PT. The presentation will be ... 30 days. Management will also be available at the ...
(Date:11/25/2015)... (PRWEB) , ... November 25, 2015 , ... ... and the Organization of Black Aerospace Professionals (OPBAP) has been formalized with the ... other AMA team leaders met with OPBAP leaders Capt. Karl Minter and Capt. ...
(Date:11/25/2015)... ... November 25, 2015 , ... Jessica Richman and Zachary ... in their initial angel funding process. Now, they are paying it forward to ... early stage investments in the microbiome space. In this, they join other ...
Breaking Biology Technology: