Figure 1. A group of Amazon molly (Poecilia formosa) huddled together, all a mirror image of each other due to cloning and genetic conversion.
A unique cross-species mating from nearly 100,000 years ago between a female Atlantic molly (Poecilia mexicana) and Sailfin molly (Poecilia latipinna) birthed a hybrid called the Amazon molly (Poecilia formosa) - an all-female species. While the mating of the two different species should have produced a sterile offspring, a hybrid animal that is unable to reproduce themselves, the Amazon molly possesses the ability to birth genetic clones of herself. Through an asexual reproduction process called gynogenesis, the Amazon molly mates with closely related males to trigger embryonic development. While the male’s sperm is required for the reproduction of the embryo, the male’s genetic material is bypassed and not inherited by the offspring.
Generations of clones often lead to extinction due to a lethal amount of mutations developed over time. However, scientists in 2018 sequenced the Amazon molly’s genome, uncovering a few signs of genomic degradation. Due to limited DNA sequencing technology, the reason why the Amazon molly had not experienced genetic decay was not discovered until later on, when technology that could precisely separate the fish's paired chromosomes to assess each of the ancestral parental genes was created. As a result, the scientists discovered that the Amazon molly eliminates harmful mutations through a DNA repair process known as gene conversion, where one DNA sequence replaces a homologous sequence. While the Amazon molly still accumulates mutations at a faster rate than sexually reproducing species, the discovery of this fish’s gene conversion during asexual reproduction has highlighted the advancement of sequencing tools and the ability to study mutations and genome evolution in a more precise manner.
Links:
https://www.sciencenews.org/article/sex-skipping-fish-hacks-evolution-gene
https://www.science.org/content/article/genetic-trick-helps-all-female-fish-species-escape-evolutionary-doom
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