Which part of the egg becomes the chick?

When a fertilised egg is laid it contains all the nutrients, energy, vitamins, minerals and water it needs to produce a live baby chick in 21 days provided it is incubated at the correct temperature and humidity.

When a chick hatches it will have consumed 99% of the white, between 1 and 1.5 grams of calcium and other minerals form the shell and 80% of the yolk.

The 1% of the white that is left will keep the chick moist and allow easy movement within the shell.

Below: Experiments have shown the chick makes use of calcium and minerals from the shell during development.

Using the calcium from the shell will weaken it and make it easier to emerge from the shell and the remaining 20% of the yolk is adsorbed into the body of the chick to nourish it for the first few days of life.

Does the chick come the yolk or the white?

Neither. The chick is grown from the germinal disc on the surface of the yolk. The growing embryo will make use of the yolk, white and shell as it grows.

The main source of nutrients for chicken embryo development is the yolk, which provides more than 90% of the nutrients and essential elements for embryonic organ growth and tissue formation. The egg white provides the water and protein needed to grow new tissues.

Below: This bullseye on the surface of the yolk is the germinal disc that will become the chick.

The chick grows to fill the eggshell and the yolk and white gradually diminishes in size as they are used up. Air enters the egg through the pores in the eggshell.

Just before hatching, the chick internalises the remains of the yolk which provides it the energy and nutrients it needs for the first few days of life.

Experiments have shown that a chick hatched with between 6.4 % and 27.2% of the yolk remaining. How much is left depends on the initial size of the yolk, the health of the parents and whether incubation was interrupted.

Below: You can see from this picture where the yolk is internalised by the chick.

It was also found that the water content of the yolk decreases considerable in the hours before the hatch.

The development of a chick inside an egg takes  almost exactly 21 days and during this time, the embryo will grow and develop all of its organs and tissues including down feathers and beak.