Chicken and Turkey are generally thought of as having two kinds of meat: light and dark. Light or white meat is the breast and wing portions. They contain less connective tissue and cook faster. The dark meat is the leg and thigh portions. These portions contain more connective tissue and fat and also take longer to cook. This is a problem when roasting whole birds, especially 20 lbs or more. The fact that the breast and wing portions cook faster than leg and thigh portions results in dry, overcooked light meat or undercooked dark meat.
There are a number of ways to help this problem. One method is to roast the turkey breast side down during at least the first two or three hours. This allows juices and some fat from the leg and thigh to drain into the breast to keep it from drying out. Although not as good, another method is to roast the turkey on each side for half of the cooking time. Other ways are to buy your turkey in portions such as whole, bone-in or boneless breast. No need to worry about getting the leg and thigh done.
Many recipes have been developed for poultry parts, such as wings, and boneless, skinless breasts and thighs. Fast food restaurants are also capitalizing on this craze as well as upscale establishments.