Thank you, mice, for your sacrifice.

Chief—let’s call him Chief for brevity’s sake—was so popular because his daughters were fantastic milk producers. He had great genes for milk. But, geneticists now know, he also had a single copy of a deadly mutation that spread undetected through the Holstein cow population. The mutation caused some unborn calves to die in the womb. According to a recent estimate, this single mutation ended up causing more than 500,000 spontaneous abortions and costing the dairy industry $420 million in losses. […]

The USDA team now knew something was wrong with this segment of Chief’s DNA, but they didn’t know exactly where or why. Remember, the USDA was working with genetic markers, which did not actually get at the underlying DNA sequence. So they called up Harris Lewin, who had, by chance, undertaken the then-enormously-expensive project of sequencing Chief’s entire genome a few years ago. Chief and his son Walkway Chief Mark were the first two dairy bulls to ever be sequenced.

Lewin and his post doc Heather Adams got to work. “Within 48 hours, we had a candidate,” he says. The stretch of DNA in question corresponded to the gene Apaf1, which had been well studied in mice. Brain cells in mice embryos with a faulty Apaf1 would grow out of control, until the embryo eventually died. “The reason we had a candidate so quickly was because of the tremendous investment in mouse genetics,” says Lewin. The scientists trudging through mouse genome could probably have never known an obscure gene they isolated had such a huge effect on the dairy industry.

–Sarah Zhang, The Dairy Industry Lost $420 Million From a Defective Cow Gene


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