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Man Is His Own Child’s Uncle, Says DNA Testing

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A baby boy born in Washington last year is his own cousin, geneticists found. The child’s father is a genetic chimera—a person who carries two sets of DNA. After failing several paternity tests, the man learned that “his” sperm actually belonged to a twin he had absorbed in the womb. The vanished twin, therefore, was technically the baby’s father [PDF].

Most people with chimerism will never find out. The process of absorption takes place so early in fetal development that there are rarely outward signs. Two eggs become one, and normally no one is the wiser. Sometimes a chimeric person will have two differently colored eyes. In cases when one egg is male and one is female, the resulting baby may be intersex, but even that presents in varying degrees of obviousness. The skin of some people with chimerism may even be striped or swirled where the two lines of DNA met, but again, this is rare. 

This isn’t the first case of its kind, although it is the first to focus on a father. Karen Keegan and Lydia Fairchild were the subjects of intense scrutiny after DNA tests showed that they couldn’t possibly be the mothers of their own children. Fairchild was accused of kidnapping and nearly lost her case. Only when doctors read about Keegan’s case did they consider the possibility that Fairchild might be a chimera. Genetic testing bore out the theory, and Fairchild got to keep her kids.

The parents in the most recent case first suspected something was up when their son was born, reports BuzzFeed's Dan Vergano. He was healthy, but his blood type didn’t match his father’s or his mother’s. A cheek-swab paternity test confirmed that the child’s DNA did not match his father’s. The couple, who had conceived through in vitro fertilization, worried that their fertility clinic had used a stranger’s sperm by accident.

They checked with the clinic. Staff assured them that there had been no mix-up. So whose sperm was it, exactly? The couple took their question to Stanford University geneticist Barry Starr, who runs the Ask a Geneticist website. Starr suggested a more comprehensive type of genetic testing. Those results showed that the baby was definitely related to his father—both as a nephew and a son.

But the man had no brother … not that he knew of, anyway. He did, however, have striped skin.

More tests confirmed Starr’s suspicion that the man was indeed a chimera.

As genetic testing becomes both more advanced and more commercially available, incidents like this may become common. The rise in fertility treatments will likely also contribute to the incidence of chimerism itself, since those procedures often lead to multiple births, or at least multiple fertilized eggs. For obvious reasons, scientists aren’t sure how many of us are chimeras. Only time will tell.

[h/t Buzzfeed

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Researchers Pinpoint the Genes Behind the Durian's Foul Stench
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Durian is a popular fruit in parts of southeast Asia. It's also known for having the most putrid, off-putting odor of any item sold in the produce section. Even fans of durian know why the fruit gets a bad rap, but what exactly causes its divisive scent is less obvious. Determined to find the answer, a team of researchers funded by "a group of anonymous durian lovers" mapped the fruit's genome, as reported by the BBC.

The study, published in the journal Nature Genetics [PDF], contains data from the first-ever complete genetic mapping of a durian fruit. It confirms that durian's excess stinkiness comes from sulfur, a chemical element whose scent is often compared to that of rotten eggs.

Analysis of the fruit's chemical makeup has been done in the past, so the idea that sulfur is a major contributor to its signature smell is nothing new. What is new is the identification of the specific class of sulfur-producing genes. These genes pump out sulfur at a "turbocharged" rate, which explains why the stench is powerful enough to have durian banned in some public areas. It may seem like the smell is a defense mechanism to ward off predators, but the study authors write that it's meant to have the opposite effect. According to the paper, "it is possible that linking odor and ripening may provide an evolutionary advantage for durian in facilitating fruit dispersal." In other words, the scent attracts hungry primates that help spread the seeds of ripe durian fruits by consuming them.

The revelation opens the door to genetically modified durian that are tweaked to produce less sulfur and therefore have a milder taste and smell. But such a product would likely inspire outrage from the food's passionate fans. While the flavor profile has been compared to rotten garbage and dead animal meat, it's also been praised for its "overtones of hazelnut, apricot, caramelized banana, and egg custard" by those who appreciate its unique character.

[h/t BBC]

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Why DNA Is So Hard to Visualize
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Picture a strand of DNA and the image you see will likely be similar to the artist’s rendering above. The iconic twisted ladder, or double-helix structure, was first revealed in a photo captured by Rosalind Franklin in the 1950s, but this popular visualization only tells part of the story of DNA. In the video below, It’s Okay to Be Smart explains a more accurate way to imagine the blueprints of life.

Even with sophisticated lab equipment, DNA isn’t easy to study. That’s because a strand of the stuff is just 2 nanometers wide, which is smaller than a wavelength of light. Researchers can use electron microscopes to observe the genetic material or x-rays like Rosalind Franklin did, but even these tools paint a flawed picture. The best method scientists have come up with to visualize DNA as it exists inside our cells is computer modeling.

By rendering a 3D image of a genome on a computer, we can see that DNA isn’t just a bunch of free-floating squiggles. Most of the time the strands sit tightly wound in a well-organized web inside the nucleus. These balls of genes are efficient, packing 2 meters of DNA into a space just 10 millionths of a meter across. So if you ever see a giant sculpture inspired by an elegant double-helix structure, imagine it folded into a space smaller than a shoe box to get closer to the truth.

[h/t It’s Okay to Be Smart]

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