Evolution: strange changes in DNA form (Introduction)

by David Turell , Saturday, November 06, 2021, 14:15 (903 days ago) @ David Turell

Strange DNA forms found in reptiles:

https://newsroom.unsw.edu.au/news/science-tech/dust-specks-which-are-actually-building-...

"Scientists have discovered that tiny ‘microchromosomes’ in birds and reptiles are the same as the tiny chromosomes in a spineless fish-like ancestor that lived 684 million years ago.

"When these little microchromosomes were first seen under the microscope, scientists thought they were just specks of dust scattered among the larger bird chromosomes, but they are actually proper chromosomes with many genes on them.

"They prove to be the building blocks of all animal genomes, but underwent a ‘dizzying rearrangement’ in mammals, including humans.

***

“'Not only are they the same in each species, but they crowd together in the centre of the nucleus where they physically interact with each other, suggesting functional coherence,” Dr Waters says.

“'This strange behaviour is not true of the large chromosomes in our genomes.”

***

“'We lined up these sequences from birds, turtles, snakes and lizards, platypus and humans and compared them,” she says.

“'Astonishingly, the microchromosomes were the same across all bird and reptile species.”

“'Even more astonishingly, they were the same as the tiny chromosomes of Amphioxus – a little fish-like animal with no backbone that last shared a common ancestor with vertebrates 684 million years ago.”

"Prof Graves says in marsupial and placental mammals these ancient genetic remnants are split up into little patches on our big, supposedly normal, chromosomes.

"'Mammal genomes have been hammered when compared to other vertebrates.”

"The findings highlight the need to rethink how we view the human genome.

“'Rather than being ‘normal’, chromosomes of humans and other mammals were puffed up with lots of ‘junk DNA’ and scrambled in many different ways,” Prof Graves says.

“'The new knowledge helps explain why there is such a large range of mammals with vastly different genomes inhabiting every corner of our planet.

Comment: Now great gaps in DNA forms of organization. This can be added to the great Cambrian gap in body form. Another gap problem is the issue of Old and New World monkeys appearance in the time record with the Africa/South America split long before:

https://academic.oup.com/mbe/article/20/10/1620/1164065

"the vicariant scenario for the origin of Platyrrhini from primitive prosimian stocks in Gondwanaland seems improbable because the separation of Africa and South America happened between 120 and 100 MYA and our divergence time dates a much younger split. Therefore, the assumption that Platyrrhini ancestors dispersed to the South American island continent at about the Eocene-Oligocene boundary seems likely, but a source continent must be elected."

Comment: the appearance of New World monkeys is estimated at 35-70 million years ago. Gaps are everywhere.