Two chicks can't come out of same egg

Gustavo Avila, 12, a soon-to-be seventh-grader at West Oak Middle School in Mundelein, asks: "How does a double yolk develop in an egg and if it were fertile would twins hatch?"

An egg is the beginning of almost all life forms. A fertilized egg becomes a baby.

Chickens lay eggs and the egg-laying females are called hens. Mature hens lay eggs almost every day. Instinct directs hens to lay a clutch or brood of eggs - about 12 in all. Once the brood is laid, the hen sits on the eggs to keep them warm. Baby chicks begin to peck through their shells after three weeks. Throughout their lifetime, hens can lay as many as 300 eggs.

Hens begin laying eggs at four months of age. The first few cycles are likely to produce twin yolks until the hen is fully mature. Double yolks also can occur when hens lay eggs too rapidly, which can be a sign of immaturity. Laying double yolks sometimes is an inherited trait.

"It's a timing mechanism," said Vickie Brown, 4-H youth educator at the Lake County Cooperative Extension office in Grayslake. "Only a small percentage of eggs produce the double yolk, and two chicks couldn't hatch in one shell," Brown said. "The record yolks in one egg shell is 9," she added.

4-H is a not-for-profit organization that fosters personal growth through various educational experiences including farming, science, citizenship and other learning opportunities. 4-H offers instructional activities to youth ages 4 to 19.

Learn more about eggs through the 4-H "Incubation and Embryology" program. Lesson plans, activities and resources can be found online at extension.uiuc.edu/lake/4hyouth.html. Or visit the 4-H exhibits at the Lake County Fair starting Tuesday, July 28, through Saturday, Aug. 2, at the Lake County Fairground in Grayslake.

"We'll have over 400 exhibits, from youth visual arts to electricity, woodworking, clothing, foods and rocketry."