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Science snapshots: Chromosomes, crystals, and drones

July 25, 2019

Exploring Human Origins in the Uncharted Territory of Our Chromosomes

A group of geneticists from Berkeley Lab, UC Davis, UC Santa Cruz, and UC Berkeley are unraveling new details about human evolution by studying the uniquely regulated portion of our chromosomes that surround the centromeres.

These stretches of DNA - termed centromere-proximal regions (CPRs) - are largely composed of highly repetitive, mostly non-gene-coding sequences that are protected from sequence shuffling during reproductive cell division.

Hypothesizing that these protected genomic regions might generate large haplotypes (groups of neighboring genes and sequences that are inherited as a single unit from generation to generation), Berkeley Lab researcher Sasha Langley and her co-authors used a database of diverse modern human genomes to investigate variation in CPRs.

Their analysis, published in eLife, revealed that centromere haplotypes - or "cenhaps" - are indeed present. Like other parts of the genome, cenhaps harbor genetic material, including functional genes, introduced when our ancestors hybridized with other hominin species; yet these sequences are surprisingly massive compared with other archaic genetic remnants.

"Interestingly, one of the Neanderthal cenhaps contains a lot of unique variation in genes that shape our sense of smell," said Langley. "And in some individuals, we found evidence of an even more ancient cenhap that appears to be derived from a previously unknown early hominin relative."

The authors conclude that cenhaps provide a great tool for exploring functional differences in CPRs and the history of early hominins, even when available fossils contain limited intact DNA.

Crystal With a Twist: Scientists Grow Spiraling New Material

With a simple twist of the fingers, one can create a beautiful spiral from a deck of cards. In the same way, scientists at Berkeley Lab and UC Berkeley have created new inorganic crystals made of stacks of atomically thin sheets that unexpectedly spiral like a nanoscale card deck.

Their surprising structures, reported in a new study in the journal Nature, may yield unique optical, electronic and thermal properties, including superconductivity, the researchers say.

These helical crystals are made of stacked layers of germanium sulfide, a semiconductor material that, like graphene, readily forms sheets that are only a few atoms thick. Such "nanosheets" are usually referred to as "2D materials."

X-ray analyses for the study were performed at Berkeley Lab's Advanced Light Source, and the crystal's twist angles were measured at the Molecular Foundry.

"No one expected 2D materials to grow in such a way. It's like a surprise gift," said Jie Yao, a faculty scientist in Berkeley Lab's Materials Sciences Division and assistant professor of materials science and engineering at UC Berkeley. "We believe that it may bring great opportunities for materials research."

Read the original UC Berkeley news release by Kara Manke.

Drones Will Fly for Days With This New Technology

Researchers with Berkeley Lab and UC Berkeley just broke another record in thermophotovoltaic efficiency, an achievement that could lead to ultralight engines that can power drones for days.

For the past 15 years, the efficiency of converting heat into electricity with thermophotovoltaics - an ultralight alternative power source that could allow drones and other unmanned aerial vehicles to operate continuously for days - has been stalled at 23 percent.

Recently, the team of researchers led by corresponding author Eli Yablonovitch recognized that a highly reflective mirror installed on the back of a photovoltaic cell can reflect low energy infrared photons to reheat the thermal source, providing a second chance for a high-energy photon to be created and generate electricity. This groundbreaking discovery - reported on July 16 in the Proceedings of the National Academy of Sciences - has allowed the researchers to raise the efficiency of thermophotovoltaics to an unprecedented 29 percent.

According to Yablonovitch, who is a senior faculty scientist in Berkeley Lab's Materials Sciences Division and a professor of electrical engineering and computer science at UC Berkeley, the current study builds on work that he and students published in 2011, which found that the key to boosting solar cell efficiency is, counterintuitively, by externally extracting light from an intense internal luminescent photon gas.

The researchers are now aiming to reach 50 percent thermophotovoltaic efficiency in the future by applying these new scientific concepts.

Read the original UC Berkeley news release by Linda Vu.

DOE/Lawrence Berkeley National Laboratory

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