Genome complexity: discarding DNA in embryology (Introduction)

by David Turell , Saturday, October 23, 2021, 16:29 (908 days ago) @ David Turell

A logical event:

https://knowablemagazine.org/article/living-world/2021/the-curious-case-shrinking-genome

"...the fungus gnat does something bizarre. Early in the embryo’s development, most of the cells jettison two specific chromosomes — enormous ones, compared with the others — so the pair never ends up in the lion’s share of the gnat’s body. Only the cells that become germ cells retain the bonus DNA and pass it on to the next generation.

"How and why this feature evolved remains largely mysterious, though biologists first spotted it a century ago. And black-winged fungus gnats aren’t the only genetic screwballs. A surprisingly wide array of creatures, all the way up to some vertebrates, dump significant stretches of DNA during early development, so the stretches don’t end up in most of their body cells.

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"To date, scientists have observed the phenomenon in various insects, in lampreys and hagfish, in hairy one-celled life forms called ciliates, in parasitic roundworms and tiny crustaceans called copepods. They’ve seen it in rat-like marsupials called bandicoots and in songbirds — probably all songbirds, according to recent work. And they expect to find many more cases.

“'A lot of these weird genomic features tend to be fairly rare, but they do evolve repeatedly,” Ross says. “It’s not just one freak event.” Presumably, then, there must be some selective advantage to the creatures that go down that evolutionary route. But what is it?

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"Guaranteeing that genes are active at certain times but not others, or in some tissues but not others, is a critical function for any living thing. Think of the many different cell types in our bodies: All contain the same DNA sequence, but our heart cells produce different proteins than our skin cells do, so that each can do its specialized job. And even within a particular type of cell, the proteins that are produced vary during a creature’s lifespan.

"Perhaps what these dropped genes do would be so damaging to adult cells that eliminating them is a better-safe-than-sorry device, Davis says. “It’s total speculation, though — because there’s no proof of anything.'”

Comment: Makes perfect sense. Much of the DNA that drives the developing fetus are not needed during regular developed life. So just keep them in germ cells.