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Synthetic Biology


Science tackles chicken feet and chicken sex

by Manny I. Fox Morone
July 9, 2023 | A version of this story appeared in Volume 101, Issue 22


An egg sitting in an egg tray with a suction cup and hose attached to its top.
Credit: Sensit Ventures
Tough to crack: Determining an egg’s sex isn’t easy, but this vacuum suction cup could be part of the solution.

Go suck an egg

Tom Turpen has been engrossed by eggs since 2019. “The eggshell is just an amazing structure,” he says. “They’re like little high-tech Wiffle balls.” Turpen, the CEO of Sensit Ventures, is referring to eggshells’ microscopically porous structure, which has evolved to let oxygen and other gases in and out of the egg so that developing chicks can breathe. He’s leveraging this oological quirk to design a machine that can suck molecules out of the pores of a chicken egg and find out the sex of the embryo inside.

Turpen’s chicken-sexing vacuum machine is part of an entry for the Egg-Tech Prize, a contest put on by the Foundation for Food and Agriculture Research. The foundation is challenging researchers to find noninvasive ways to differentiate male and female eggs before they hatch. Nearly all males have historically been culled and disposed of a few days after hatching, because they can’t lay eggs and don’t produce as much meat as their female siblings. The practice has raised an animal welfare issue and wastes eggs that could be used as food or for vaccine production. It also consumes lots of energy to incubate eggs that will ultimately be thrown out.

Turpen teamed up with Cristina Davis, an engineer and chemical sensing scientist at the University of California, Davis, to work out how to link the sex of an embryo growing inside an egg to the volatile organic compounds (VOCs) that the egg releases through its pores. “VOCs represent the endpoint of the physiology changes that are happening inside of the system,” Davis says. So the team figured that different sexes might give off distinct bouquets of VOCs.

By hooking up a vacuum-enabled suction cup to an egg, the team pulled VOCs through the porous shell and analyzed those chemicals using gas chromatography/mass spectrometry. All said, the group has developed a model that, after 2 min of sucking, can use VOC data to statistically separate male and female eggs with 80% accuracy (PLOS One 2023, DOI: 10.1371/journal.pone.0285726).

Turpen tells Newscripts that the Egg-Tech Prize is looking for accuracies closer to 98%, the rate achievable by human sexers post-hatching. An eventual commercial version of the suction cup method would use robotics and advanced data handling to match the speed of humans, who can sex a hatched chick in a few seconds. So Turpen’s team is still tweaking its contest entry in hopes of ruling the roost and snagging the $4 million prize.


A limp chicken foot with yellow fluffy feathers sprouting out of it.
Credit: R. Cooper & M.C. Milinkovitch © University of Geneva, Switzerland
Who put that there? The scales on a chicken's feet can be turned into feathers.

Feet of a feather

Michel Milinkovitch’s genetics and evolution lab at the University of Geneva might remind a visitor of a mad scientist’s haunt. It holds hundreds of living animal specimens, some of which have been genetically modified or otherwise tweaked as part of the lab’s work to understand the complexity of nature and evolution. One of the lab’s latest creations is a feather-footed chicken.

The researchers found that injecting an embryo with a small molecule called smoothened agonist caused chickens to develop feather follicles on their feet where scales would normally be (Sci. Adv. 2023, DOI: 10.1126/sciadv.adg9619). The molecule works by activating the Sonic hedgehog signaling pathway, a protein pathway that triggers a slew of different steps in development. Treatment during a sweet spot of embryo growth appears to produce extra-feathery but otherwise normal chickens.

This Newscriptster—and most of the world, surely—wonders why anyone would want a chicken with more fluff to begin with. To this, Milinkovitch says that the work is still basic science, an early step in understanding how various animals developed their fundamental features, like scales, feathers, hair, and skin. “We are a little bit less stupid now,” he says. “We are still very stupid, but we are a bit less stupid by understanding better how you can make a scale or a feather.”

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