Evolution: speciation related to satellite (junk) DNA (Introduction)

by David Turell , Monday, August 23, 2021, 19:09 (977 days ago) @ David Turell

Species within a family are designated by their differing Satellite (junk) DNA:

https://phys.org/news/2021-08-so-called-junk-dna-key-role.html

"More than 10 percent of our genome is made up of repetitive, seemingly nonsensical stretches of genetic material called satellite DNA that do not code for any proteins. In the past, some scientists have referred to this DNA as "genomic junk."

"Over a series of papers spanning several years, however, Whitehead Institute Member Yukiko Yamashita and colleagues have made the case that satellite DNA is not junk, but instead has an essential role in the cell: it works with cellular proteins to keep all of a cell's individual chromosomes together in a single nucleus.

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[They] "take these studies a step further, proposing that the system of chromosomal organization made possible by satellite DNA is one reason that organisms from different species cannot produce viable offspring.

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"Researchers have known for years that satellite DNA is highly variable between species. "If you look at the chimpanzee genome and the human genome, the protein coding regions are, like, 98 percent, 99 percent identical," she says. "But the junk DNA part is very, very different."

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"When the researchers deleted a protein called Prod that binds to a specific satellite DNA sequence in the fruit fly Drosophila melanogaster, the flies' chromosomes scattered outside of the nucleus into tiny globs of cellular material called micronuclei, and the flies died. "But we realized at this point that this [piece of] satellite DNA that was bound by the Prod protein was completely missing in the nearest relatives of Drosophila melanogaster," Jagannathan said. "It completely doesn't exist. So that's an interesting little problem."

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"Taken together, these findings suggest that because satellite DNA mutates relatively frequently, the proteins that bind the satellite DNA and keep chromosomes together must evolve to keep up, leading each species to develop their own "strategy" for working with the satellite DNA. When two organisms with different strategies interbreed, a clash occurs, leading the chromosomes to scatter outside of the nucleus."

Comment: Species differences are maintained by their differing satellite/junk DNA. Another clue as to how speciation happens by genome changes.