We may be another step closer to discovering what makes us human.

A new study published online this week in Genome Research has pinpointed three genes in humans that may genetically differentiate us from chimps and other primates. Genetically we are very similar to chimps, so most of the differences researchers have observed to date regard physical appearance and behaviors.

The new study found several genes that were once silent and nonfunctional in our primate ancestors, and seem to have awakened around the time that humans formed a new evolutionary branch.

Researchers at the University of Dublin compared sections of the human genome with those of chimps and other primates to find active genes that are absent from the chimp genome. They found three human genes, CLLU1, C22orf45 and DNAHI0OS, that were present but inactive in non-human primates.

At the location of each of the three human genes, a disabling sequence of DNA was found in the genomes of the chimp, macaque, gorilla, gibbon and partially in the orangutan. The study suggests that the awakened human genes not only shed their disabling components, but gained “enabling” sequences that helped them do the work of forming proteins in the body.

Previous research found that genes arising from inactive DNA were present in flies and yeast. The study suggests there may be a total of 18 awakened genes in humans, but researchers were limited to analyzing only a part of the 24,000-gene human genome.

The functions of these novel genes are not yet known, but it is tempting to infer that these genes, specific to humans, are responsible for the attributes that differentiate us from other primates.

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Before efforts to sequence the human genome began, scientists thought they’d find about 100,000 protein coding genes in the three billion bases pairs of DNA that are found in almost every cell. But much to everyone’s surprise, the true number turned out to be much lower. It’s now thought that the human genome contains only about 20,000 protein-coding genes, representing less than 2% of the contents of the genome.

Much of the remaining 98% of the genome remains a mystery. Some chunks of this DNA are referred to as “ultraconserved elements” because they have remained practically unchanged through hundreds of millions of years of evolution in many species.

It is a basic principle of biology that if something goes unchanged for that long, it ought to be good for something. Yet the function of ultraconserved elements is completely unknown. In fact, laboratory studies in mice have shown that the animals do just fine when some of the ultraconserved elements are deleted.

To find out if ultraconserved elements really are dispensable, Cory McLean and Gill Bejerano of Stanford University analyzed ultraconserved elements and non-conserved DNA sequences in five mammalian genomes.

Their results, published online today in Genome Research, show that regions of DNA that are identical or very similar between humans, macaques, and dogs are about 300 times less likely to be missing in rats and mice than regions that are not as closely conserved between the primate and dog species.

It’s not that ultraconserved regions are somehow protected from change. The researchers suggest that in the wild, mutations in these elements put affected animals at a disadvantage, causing the changes to be swept away over time by natural selection. But in the lab there isn’t a whole lot of natural selection — in an environment where mice are treated to filtered air, an absence of predators, and all the food and water they could ever want, any loss of fitness due to lost ultraconserved elements doesn’t seem to have any observable consequences.

McLean and Bejerano also found that DNA sequences that can be traced farther back in evolutionary time are more likely to be conserved in diverse species today.

“The longer the sequence has been in us, the less likely it is to be lost. It’s almost like the bricks in the foundation of a building, which hold up the rest of the structure,” said Bejerano in a statement.

Detailed new genome sequences from a variety of mammals will allow Bejerano’s research team to further analyze ultraconserved elements and perhaps ultimately understand what it is they are doing in the genome.

“Evolution is a lot of fun,” said Bejerano. “You answer one question, and five others pop up. But one of the most rewarding things to me is the fact that we’re developing a growing appreciation for how much these regions actually matter.”

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Just four simple ingredients — water, malt, hops, and yeast – go into making beer, a delicious and intoxicating brew that has been enjoyed for the past 6000 years.

The yeast not only ferments sugars into alcohol, but also affects the appearance, aroma and taste of a beer. It’s not surprising then that each brewery maintains it own unique yeast strains. These strains, however, can be broken down into two main types: ale yeasts and lager yeasts.

It’s been known for some time that lager yeast is a genetic mix of yeast species S. cerevisiae (the same species ale yeasts hail from) and another species, S. bayanus. But the results of a new Stanford study that will be published online Thursday in Genome Research are the first to show that this mixing of DNA actually happened twice during the history of lager, and that the strain of S. cerevisiae involved was an ale yeast both times.

“We were excited to find this connection, because it makes so much sense,” said Gavin Sherlock,one of the study’s authors, in a statement. “The same breweries were used for both ale and lager, so it was really gratifying.”

Lager beers are brewed at much cooler temperatures than ales (52-58° F vs. 64-70° F), a tradition that dates back to Bavarian brewers who stored their beer in icy caves in the Alps during the summer months.

“It’s possible that the ale strain provides a certain flavor profile, while the second strain conferred the ability to ferment at cooler temperatures,” said Barbara Dunn, the other study author, referring to the hybridization events that created lager yeasts.

“Mixing them together is a nice way for the yeast to double its genetic options.”

When the researchers looked at yeast descended from the two groups of lager yeast, they saw further variation between strains.

“The fact that lager yeasts isolated from different breweries each seem to have a unique genomic make-up may indicate that the yeasts are adapting to the conditions specific to each brewery,” explained Dunn.

“Our discovery that unique genomic structures may be characteristic of each brewery and/or beer type could lead to insights on how to directly control flavor and aroma in beer.”

That’s the kind of science we can all raise a glass to.

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