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Simple eggs with little yolk are called microlecithal, medium-sized eggs with some yolk are called mesolecithal, and large eggs with a large concentrated yolk are called macrolecithal. [7] This classification of eggs is based on the eggs of chordates, though the basic principle extends to the whole animal kingdom.
The chicken (Gallus gallus domesticus) is a large and round short-winged bird, domesticated from the red junglefowl of Southeast Asia around 8,000 years ago. Most chickens are raised for food, providing meat and eggs; others are kept as pets [1] or for cockfighting.
As is the case with chickens, various breeds have been developed, selected for egg-laying ability, fast growth, and a well-covered carcase. The most common commercial breed in the United Kingdom and the United States is the Pekin duck , which can lay 200 eggs a year and can reach a weight of 3.5 kg (7 lb 11 oz) in 44 days. [ 34 ]
The physical traits used to distinguish chicken breeds are size, plumage color, comb type, skin color, number of toes, amount of feathering, egg color, and place of origin. [1] They are also roughly divided by primary use, whether for eggs, meat, or ornamental purposes, and with some considered to be dual-purpose. [1]
This chicken egg has been soaked in vinegar for a few days and has become translucent and flexible. Anatomy of a chicken egg. The bird egg is a fertilized gamete (or, in the case of some birds, such as chickens, possibly unfertilized) located on the yolk surface and surrounded by albumen, or egg white. The albumen in turn is surrounded by two ...
Medium white eggs in carton. Chicken eggs are graded by size, for the purpose of sales. The egg shell constitutes 8–9% of the weight of the egg (calculated from data in Table 2, F. H. Harms). [1] A scale for grading eggs. An egg scale that was patented in 1924
The chicken breeds recognized by the American Poultry Association are listed in the American Standard of Perfection. They are categorized into classes: standard-sized breeds are grouped by type or by place of origin, while bantam breeds are classified according to type or physical characteristics.
The egg is not retained in the body for most of the period of development of the embryo within the egg, which is the main distinction between oviparity and ovoviviparity. [1] Oviparity occurs in all birds, most reptiles, some fishes, and most arthropods. Among mammals, monotremes (four species of echidna, and the platypus) are uniquely oviparous.