The Amazon Molly

     

The Amazon Molly is an all-female freshwater fish species found in southern Texas and Mexico. The Amazon Molly resulted from a cross between the Atlantic Molly and the Sailfin Molly. When Amazon mollies reproduce, their offspring are clones of the parents’ DNA. Typically, asexual species do not survive long because there is no sexual recombination through mating. However, this species uses gene conversion, a DNA repair mechanism, to stay healthy and produce viable offspring. How does this work? The fish use a “copy and paste” method, taking specific stretches of genetic code from their own chromosomes and using them on others. This method works because it allows the fish to pass on beneficial traits, erase harmful mutations, and fix errors from its two parent species. Without the ability to purge harmful mutations through sexual reproduction, the Amazon Molly “avoids accumulating harmful mutations by shuffling its own genome around” (Schartl, 2026).

Picture/Article: https://www.sciencenews.org/article/sex-skipping-fish-hacks-evolution-gene 

Second Article: https://www.lmu.de/en/newsroom/news-overview/news/how-a-clonal-fish-avoids-genetic-decay-752cd04a.html 

A Fish That Skips Sex and Still Survives: A Genetic Mystery

                 Most species rely on sexual reproduction to mix genes and maintain healthy genetic diversity. However, scientists have discovered a unique fish species that appears to survive without traditional reproduction. The Amazon molly, an all-female fish species, reproduces through a process called gynogenesis. This is where the presence of sperm from a related species triggers reproduction but the sperm’s DNA is not actually incorporated into the offspring.

Normally, species that reproduce without mixing genes are expected to accumulate harmful mutations over time. Without the genetic variation created by sexual reproduction, these mutations can accumulate and eventually threaten the survival of the species. Because of this, scientists once believed that asexual species would not survive for long periods of time.

Recent research has revealed that the Amazon molly may avoid this problem through a genetic process known as gene conversion. Gene conversion is a mechanism where DNA sequences can be copied from one chromosome to another, effectively repairing or replacing damaged genetic information. This process allows the fish to remove some harmful mutations and maintain a relatively healthy genome.

                                 

This discovery is significant because it challenges long-standing ideas about evolution and reproduction. Scientists previously believed that sexual reproduction was essential for long-term survival because it helps prevent the buildup of harmful mutations. However, the Amazon molly has existed for more than 100,000 years, suggesting that alternative genetic mechanisms can help maintain genetic stability.

Understanding how gene conversion works in this species could help scientists learn more about how genomes repair themselves and how evolution can occur in unexpected ways. This research may also provide insights into how genetic mutations are managed in other organisms, including humans.

Source: 

https://www.sciencenews.org/article/sex-skipping-fish-hacks-evolution-gene

Additional Link: 

https://medlineplus.gov/genetics/understanding/mutationsanddisorders/

Evolution and the Genome

A group of researchers from joined together in California to analyse the human genome and compare it to the chimpanzee genome. The goal was to look at gene conversions and recombination frequencies to analyze the process of evolution. In classical models it is found that mutation, recombination, and natural selection are the driving forces, this model uses a force called GC-biased gene conversion(gBGC). The basic principle is that recombination favor a (G/C) conversion over a (A/T) conversion. The (G/C) are the bases guanine and cytosine. The (A/T) are the based adenine and thymine. So when there is a mismatch and it is being resolved, the (G/C) bases are favored by natural processes.

The driving force for evolution in the model is a sub-group for recombination. Upon carrying out the experiment of applying the model to the human genome and chimpanzee genome, it was found that the human genome gBCG tracts show that the gene conversion has been a major player in the recent evolution in humans. If we could possibly control the re-combinations and the gene conversions which occur, we could possibly dictate human evolution.

http://web.ebscohost.com/ehost/pdfviewer/pdfviewer?sid=cc3f334a-9743-4c1c-9b4b-6c1cfa5d9ec9%40sessionmgr14&vid=4&hid=28

http://www.ncbi.nlm.nih.gov/pubmed/19630562

Reference
Capra JA, Hubisz MJ, Kostka D, Pollard KS, Siepel A (2013) A Model-Based Analysis of GC-Biased Gene Conversion in the Human and Chimpanzee Genomes. PLoS Genet 9(8): e1003684. doi:10.1371/journal.pgen.1003684