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| The image above shows the exoskeletons of a normal mosquito larva on the left and a mosquito larva with the gooseberry gene edited out on the right. Credit: Alys Jarvela/University of Maryland. |
The bad week for Creationism is continuing. This time a sacred dogma bites the dust as scientists from Maryland University, USA, show that mosquitoes evolved with a loss of genes - something that Creationists tell their dupes is impossible, despite the evidence from parasitology of evolution by reduction in complexity.
The initial discovery of the missing gene, known to entomologists as paired, was made by the lead researcher, Alys M. Cheatle Jarvela when she was looking for it in mosquitoes to use as a standard for comparison to the genes she was studying in crickets. Paired is found in almost all segmented arthropods and it controls the growth of repeated segments during development. If it is deactivated in fruit flies, for example, every alternate segment fails to develop and the developing embryo dies.
Having discovered that paired was missing, the team changed direction to investigate how segmentation is maintained in the absence of this controlling gene in developing mosquitoes. They built on a 1996 work which showed that when paired is deactivated in fruit flies, a closely related gene, gooseberry can be manipulated to serve the same purpose and the fruit flies develop normally. This situation was genetically engineered and depended on the fact that gene duplication can provide a 'spare' gene that can evolve a new role without loss of function of the old role. The question was, had this happened naturally in an ancestral mosquito? Since paired is present in a fly related to mosquitoes, this divergence must have happened relatively recently in the stem mosquitoes.
To test the hypothesis that gooseberry had assumed the role of paired in mosquitoes, the team knocked out the gooseberry gene in developing Anopheles stephensi mosquitoes. The result was that these modified mosquitoes developed similarly to the fruit flies with missing paired genes, showing that gooseberry had indeed evolved to fill the roll of paired. The results are published open access in Communications Biology:
Abstract
Regulatory genes are often multifunctional and constrained, which results in evolutionary conservation. It is difficult to understand how a regulatory gene could be lost from one species’ genome when it is essential for viability in closely related species. The gene paired is a classic Drosophila pair-rule gene, required for formation of alternate body segments in diverse insect species. Surprisingly, paired was lost in mosquitoes without disrupting body patterning. Here, we demonstrate that a paired family member, gooseberry, has acquired paired-like expression in the malaria mosquito Anopheles stephensi. Anopheles-gooseberry CRISPR-Cas9 knock-out mutants display pair-rule phenotypes and alteration of target gene expression similar to what is seen in Drosophila and beetle paired mutants. Thus, paired was functionally replaced by the related gene, gooseberry, in mosquitoes. Our findings document a rare example of a functional replacement of an essential regulatory gene and provide a mechanistic explanation of how such loss can occur.
Cheatle Jarvela, A.M., Trelstad, C.S. & Pick, L.
Regulatory gene function handoff allows essential gene loss in mosquitoes.
Commun Biol 3, 540 (2020). https://doi.org/10.1038/s42003-020-01203-w
Copyright: © 2020 The autors, published by Springer Nature
Open access
Reprinted under Creative Commons Attribution 4.0 International License (CC By 4.0)
What this clearly shows is evidence that not only can gene duplication provide new genetic material that evolution can work on and repurpose, but that evolution can involve a loss of genetic information. This entirely refutes claims by Creationists such as Michael J Behe, for example, that mutations are always degenerative, that no new information can arise by mutation and that loss of genetic information is invariably fatal.
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