Post Flood Rapid Diversification
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Post Flood Rapid Diversification
an Australian research group has now proposed that retroelements are involved in mammalian speciation. The researchers were studying an infertile hybrid wallaby they had found in a wildlife park—a result of crossing two different species: the swamp wallaby and the tammar wallaby. They looked at the genome of this unusual hybrid marsupial, because: 1.there are genetic models that predict that rearrangements in the genomes of hybrids can aid reproductive isolation, by preventing hybrid and parent species crossing, leading to the formation of new species,7 and 2.TEs can cause DNA rearrangements in hybrid fruit flies. They found that a retroelement had jumped profusely in the genome of the hybrid wallaby, and had integrated around the chromosome centromeres—the region on the chromosome to which the spindle fibres attach during cell division. One of the researchers commented: We thought it took millions of years of long-term selection for a jumping gene to be activated. Weve now shown that it can happen maybe in five minutes after fertilisation. The finding indicated also that the jumping gene in the hybrid had probably been reconstructed (and reactivated) by the genetic combination of two incomplete, inactive segments of a retroelement present in one or both of the parents. This has previously been reported in mice. Since DNA methylation (the linking of a methyl group to the nucleotide bases adenine or cytosine) is important for switching off genes, it is believed that this process is also used by host cells to stop the movement of TEs. Deficient methylation would then enable jumping. The researchers found that the retroelements in the DNA of the hybrid were indeed unmethylated. This was also the case in two additional hybrids, each from an independent mating between two different wallaby species. The researchers suggested that the ability of retroelements to produce genomic rearrangements in hybrid wallabies, due to deficient methylation (eventually resulting in the formation of new species) may be a widespread phenomenon in hybrid mammals. However, this idea has now been challenged by another research group, who did not find any methylation changes in the genomes of a number of mammalian hybrids they studied.12 The very rapid genetic changes caused by TEs could help explain the formation of the variants from the original kinds on Noahs Ark in the relatively short biblical time frame.1 Rapid speciation apparently occurred, since early historical records already show a large variety of types similar to those present today. The various species representing the variants in e.g. the kangaroo/wallaby created kind would all then stem from the original parent kind present on the Ark. Based on the rapid jumping of retroelements in hybrid wallabies and fruit flies, on their ability to cause DNA rearrangements, and on their role in gene regulation, it is plausible that these TEs were active in the past, and were an original mechanism for expressing Gods programmed variation within kinds. Today, the presence of incomplete, inactive segments of retroelements in wallaby chromosomes, which probably recombined in the hybrid to form active elements, as in the case of hybrid mice, may be vestiges from this past mechanism. Are retroelements involved in wallaby speciation today? The wallaby crosses described here only produce sterile males, a result which is common in interspecific hybridization in mammals. Therefore, most male hybrids cannot produce offspring with female hybrids from a compatible crossing. In the unlikely event of a fertile male successfully mating, there is also no certainty that this will produce viable offspring. These obvious problems, and the fact that TEs are mostly inactive today and are only jump started by the unlikely events of crossing between species, indicates that the role of retroelements in speciation has been either greatly reduced or has stopped altogether Taken for TJ
YouTube | December 16, 2008
