BioQuakes

AP Biology class blog for discussing current research in Biology

Author: sejeology

Preferential Gene Expression: Not As Random As We Thought

Our conventional knowledge of genetics dictates that the activation of genes in our DNA is random. It is equally likely that our body will express our mother’s alleles as it is that our body will express our father’s. In the case that one parent donates a defective copy, it will be silenced; the other parent’s healthy set of DNA takes precedence and becomes activated.

However, a new study indicates that gene expression and activation is not as random as we thought. In certain regions of the body, our genes demonstrate preferential expression.

A team of scientists at the University of Utah found that almost 85 percent of genes in juvenile mice brains displayed preferential treatment. The mice brains activated one parent’s set of DNA over the other’s. This phenomenon was observed in other areas of the body, as well as in primates.

Although the preferential expression came to a close within ten days, it could provide explanations for vulnerability to brain diseases such as schizophrenia, ADD, and Huntington’s. The temporary preferential treatment to one parent’s copy of DNA could trigger a host of problems specific to that cell site that lead to such disorders, if the parent had given a defective copy of genes.

The study has the potential to alter our basic understandings of genetics, and how we are more prone to certain specialized diseases.

Image: (Public Domain, https://pixabay.com/en/dna-biology-medicine-gene-163466/)

Hunter-Gatherer to Westernized Human Gut Biomes

Somewhere between the time of early hunter-gatherer humans, and the present-day humans living in modernized Western societies, the human gut biome lost much of its diversity. New research has contributed another clue as to the evolution of the human gut biome.

An international team of scientists studied the fecal samples of an intermediary group between hunter-gatherers and Westernized humans. The Bantu community in Africa is a traditional, agricultural population that has incorporated some available Western practices, including the use of antibiotics and therapeutic drugs.

 

Bantu people; Steve Evans,  https://commons.wikimedia.org/wiki/Bantu#/media/File:Mozambique001.jpg

The scientists compared the Bantu gut biomes to those of the BaAka pygmy population, who resemble early hunter-gatherer populations and have no Western influences, and to the gut biomes of humans living in modern, Westernized societies.

By analyzing the sequence data of the three human biomes, the scientists placed the Bantu’s biome composition in between the BaAka’s and Westernized humans’. The Bantu shared similar bacterial species as the BaAka, but lacked many of the traditional bacteria that the BaAka possessed. In fact, the BaAka had such a different biome composition that their gut more closely resembled wild primate biomes!

 

Based on the functions of the variable bacterial groups between the three populations, the team hypothesizes that the boosted carbohydrate-processing pathways in Bantu and American biomes is a result of the sugars in our diet, whereas the BaAka do not have much access to such foods and thus do not have such bacterial populations.

Ultimately, the scientists have accepted that our diet contributes significantly to our gut biome composition.

Evolution of Human Lifespans

human_evolution_scheme

(Locutus Borg, Wikimedia Commons)

Humans have started living longer and healthier lives. According to research conducted by various international teams, the last two centuries have had a greater percent increase in human lifespan than the past millions of years did.

The research teams compared the average lifespan of the most developed societies to the average lifespan of modern-day hunter-gatherer populations, which most closely resemble the lifespan and lifestyle of early humans. The researchers found that developed countries, such as Sweden, have average lifespans of eighty years now (an increase from the mid-thirties range it was in 200 years ago). On the other hand, hunter-gatherer populations such as the Hadza in Tanzania live only ten to twenty years longer than wild primates.

Such drastic improvements in human longevity are attributed to the advent of several post-industrial era features, including modern medicine and supermarkets. However, males trail behind females in terms of lifespan by at least three to four years– something that has not changed since the beginning of primate history.

The exact reason for the lifespan gender gap is unknown. Some hypotheses propose that males are more at-risk because they carry one X-chromosome and one Y-chromosome, as opposed to the females’ two X-chromosomes, which makes males more susceptible to disease. Another possible explanation centers around harmful male-related behavior, such as fighting. What do you think is the most likely reason for the gender gap?

Yawning and Brain Size

macaca_fuscata_juvenile_yawning

Recently, scientists discovered a correlation between yawning and brains: the longer the average duration of a specie’s yawn, the bigger that specie’s brain size,  as measured by brain weight and total number of cortical neurons.

The study was conducted on 109 individuals from across 19 different species, including cats, humans, mice, camels, and more. The investigators found that the duration of yawns was shortest in mice, who averaged 0.8 seconds, and longest in humans, who averaged 6.5 seconds. The scientists plan on investigating whether this correlation holds true amongst individual members of a species.

The study was created in response to the ideas set forth in Gallup’s 2007 paper on the thermoregulatory theory of yawning, one of the strongest theories about why we yawn (we do not yet definitively know the biological purpose of yawning). The thermoregulatory theory indicates that yawning cools down the brain in homeotherms via three potential mechanisms. But whether or not this brain-cooling is simply a side effect or the primary function of yawning is up for debate.

Based on Gallup’s paper, the investigators of this study hypothesized that longer yawns would produce greater physiological responses, in terms of blood flow and circulation to the brain– which would be evolutionarily necessary for species with larger, more complex brains.

There are other theories about why we yawn, such as a 2014 paper stating that yawning stimulates cerebrospinal fluid circulation, which in turn increases species’ alertness. A common theory that yawning increases blood oxygen levels has largely been disproved. How would such alternate theories have different implications for the discovered correlation between yawning and brain size?

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