In the 10 years since the complete human genome was published, molecular biologists have been hard at work unraveling the genomic codes of multitudes of life forms. What stands out, time and again, is how much all life shares in common, and how complex everything is. Did you know the domesticated watermelon has about as many genes as you do?
In 2012, genome researchers sequenced the DNA of an unborn human baby, the western lowland gorilla, fruits and grains, and livestock.
The Tomato, Solanum lycopersicum
The unraveled tomato genome could yield tastier fruits, improving on the mealy quality so common to the dense orbs we find in supermarkets. In May, the Tomato Genome Consortium published genome sequences for two tomatoes: The “Heinz 1706” varietal, an inbred cultivar that serves as a model for the domesticated tomato, and its closest wild counterpart, Solanum pimpinellifolium. The tomato has 35,000 genes and 12 chromosomes, and sequencing all of this took about nine years.
Barley, Hordeum vulgare
Sequencing the barley genome could potentially lead to better beer, it’s true–but more accurately, it will lead to better grains, which can more easily resist disease, survive drought and produce more kernels. Barley’s genome contains 5.1 gigabases, which is 1.3 times larger than the human genome. Sequencing all of this was difficult, because much of the plant’s genome is made up of repeating sequences. The genome published in October is actually just a draft, with all the genes present but with some specific locations unknown. As BeerSci explained, there’s still plenty of work to do before researchers can pin down how genes are activated, which would lead to designer barley.
Watermelon, Citrullus lanatus
Once again, DNA sequencing of a crop plant could help biologists and plant growers produce tastier versions of the crop. The watermelon genome has the added benefit of illuminating the plant vascular system. The genome of the domesticated watermelon contains 23,440 genes, roughly the same number of genes as in humans, according to scientists at Cornell. To decode it, the team compared the genomes of 20 different watermelons. This enabled the researchers to identify which areas of the genome have been under selection by humans, like those associated with fruit taste, size and color. Along with the previously published cucumber genome, the watermelon genome is now helping biologists determine how proteins and RNAs are involved in the plant vascular system, which could lead to drought-resistant crops.
Human Sperm Cell
In July, scientists reported the sequencing of 91 sperm cells from one man, the first complete sequencing of a human gamete cell. The 40-year-old donor already had his own genome sequenced, so this experiment was able to show recombination, the genetic mixing that ensures a baby’s DNA has genetic material from its four grandparents. The researchers, based at Stanford, noticed each individual sperm had different mixes of chromosomes. This is what causes genetic variation among offspring.
A Fetus In The Womb
Fetal genetic testing already exists for a few chromosomal disorders, like amniocentesis for Down syndrome. But in this study, researchers were able to sequence almost the entire genome of an unborn fetus in the second trimester, without interrupting the fetus or the womb. This non-invasive method could someday be commonplace– but whether it should is an open question. The team used the mother’s blood and the father’s saliva to determine their child’s genetic sequence. They had to figure out each parent’s own genetic variants, called haplotypes, which would be present on each chromosome. From there they could figure out which haplotypes came from which parent, and then they were able to determine new genetic variants that the baby wouldn’t share with either parent. Most of the time, de novo mutations are totally harmless, but sometimes they can give rise to rare genetic disorders. This image shows a human fetus at 12 weeks of pregnancy.
The Human Genome’s Dark Matter
For years after the human genome was first sequenced, scientists thought a lot of it was junk. Only about 1 percent of our genome codes for proteins that actually do anything, so the rest of our DNA has been like biology’s dark matter, acting in mysterious ways. After years of further research, geneticists now have some clarity. Actually, about 80 percent of our genome is biologically active, according to the ENCODE project, for “Encyclopedia of DNA Elements.” These non-coding regions of DNA could have major bearing on diseases and genetic mutations. Better rewrite the textbooks again.
Western Lowland Gorilla
This was the last great ape to have its genome sequenced. And it turns out that in a third of the genome, gorillas are closer to humans and chimpanzees than humans and chimps are to each other. About 500 genes have experienced accelerated evolution in gorillas, chimps and us, the study found. This is especially true for genes involved in hearing. After looking at the genomes of gorillas, chimpanzees and humans, the study authors hypothesized that gorillas split from our last common ancestor around 10 million years ago. Chimps and humans diverged about 4 million years later. Still, despite the more recent common heritage between humans and chimps, humans are more gorilla-like than we thought.
Domesticated Pig
Along with providing people with tasty food, pigs are an important research subject, standing in for humans in multitudes of biomedical studies. A new genome sequence for a domestic Duroc sow lays bare genes that may be associated with disease, researchers said. The sequence shows the rapid evolution of genes involved in smell–just like apes–and in genes related to immune response. It also shows some genetic variants that are implicated in disease, the same variants seen in humans. This affirms pigs’ value as research subjects, according to the Swine Genome Sequencing Consortium. Understanding how pigs can resist disease would help livestock producers, too.
