Research  Y chromosome is evolving faster than the X + How the brain calls up visual memories

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Y chromosome is evolving faster than the X, primate study reveals

EXCERPTS: It's not clear exactly why the Y chromosome is evolving so rapidly. For starters there is only a single copy of the Y chromosome per cell — in primates, females carry two copies of the X chromosome, while males carry an X and a Y chromosome ––the Y chromosome plays a critical role in sperm production and fertility. Having only a single copy of the Y chromosome presents a vulnerability ––if changes happen to occur, there is no second chromosome to act as a backup.

And changes are likely to occur due to something called mutation bias. The Y chromosome may be so prone to change because it generates many sperm. This requires lots of DNA replication. And every time DNA is copied, there's a chance for mistakes to creep in.

In the new study, published May 29 in the journal Nature, scientists compared the sex chromosomes of five great ape species — chimpanzees (Pan troglodytes), bonobos (Pan paniscus), western lowland gorillas (Gorilla gorilla gorilla) and Bornean and Sumatran orangutans (Pongo pygmaeus and Pongo abelii) — and one more distantly related to humans, siamang gibbons (Symphalangus syndactylus).

[...] The findings revealed that across all the studied species, the Y chromosome evolved rapidly. [...] One reason the Y seems to have thrived despite such a high rate of mutation is that across all the studied species, it contains stretches of highly repetitive genetic material, such as palindromic repeats, where the sequence reads the same forward and backward. Nestled within these stretches of repeating DNA are genes. So the repeated DNA may safeguard important genes from replication mistakes and thereby preserve essential biological material, the researchers wrote in their paper... (MORE - missing details)

How the ‘mind’s eye’ calls up visual memories from the brain

INTRO: Picture a strawberry. Most people can easily distinguish between that image in their mind’s eye and an actual strawberry. Now researchers say that they’ve worked out how the brain draws this distinction and where in the brain the process happens.

According to a study in monkeys, the key part of the brain is the primary visual cortex, which is also involved in vision. The authors found that neurons in this region displayed a different activity pattern for images conjured up from memory compared with that for real-time visual input. They conclude that the primary visual cortex is crucial for recalling images stored in memory.

“It’s an intriguing study that goes beyond what we know in several ways,” says cognitive neuroscientist Floris de Lange at Radboud University in Nijmegen, the Netherlands, who was not involved in the work. But others in the field, such as Julio Martinez-Trujillo, a cognitive neurophysiologist at Western University in London, Ontario, Canada, says that another area of the brain, the prefrontal cortex, is more likely than the visual cortex to be key for recalling images... (MORE - details)

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