The white egg yolk at left, seen next to a yellow yolk, may seem strange, but it's just a result of the chicken feed used, scientists say. Junko Kimura/Getty Images hide caption

itoggle caption Junko Kimura/Getty Images

Cage-free chickens in Harold Sensenig's barn near Hershey, Pa., get to roam and perch on steel rods, but they don't go outside. Dan Charles/NPR hide caption

itoggle caption Dan Charles/NPR

An image of researchers at Oregon Health & Science University removing the nucleus from the mother's cell before it's inserted into the donor's egg cell. Courtesty of Oregon Health & Science University hide caption

itoggle caption Courtesty of Oregon Health & Science University

A city worker sells eggs as people line up outside the truck in Mexico City on Aug. 24. The Mexican government is battling an egg shortage that has caused prices to spike in a country with the highest per-capita egg consumption on Earth. Alexandre Meneghini/AP hide caption

itoggle caption Alexandre Meneghini/AP

At the JS West egg farm, south of Modesto, Calif., one chicken house has the new, spacious cages that egg producers and animal welfare advocates say keep chickens happier. Big Dutchman hide caption

itoggle caption Big Dutchman

At the JS West egg farm, south of Modesto, Calif., one chicken house has the new, spacious cages that egg producers and animal welfare advocates say keep chickens happier. Big Dutchman hide caption

itoggle caption Big Dutchman