Sex-links are cross-bred chicken

Chicken

The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...

s whose color at hatching is differentiated by sex, thus making chick sexing

Chick sexing

Chick sexing is the method of distinguishing the sex of chicken and other hatchlings, usually by a trained person called a chick sexer or chicken sexer...

 an easier process. Sex-links come in many varieties, few of which are a true breed

Breed

A breed is a group of domestic animals or plants with a homogeneous appearance, behavior, and other characteristics that distinguish it from other animals or plants of the same species. Despite the centrality of the idea of "breeds" to animal husbandry, there is no scientifically accepted...

. As hybrids of laying or dual-purpose breeds infused with extra vigor via heterosis

Heterosis

Heterosis, or hybrid vigor, or outbreeding enhancement, is the improved or increased function of any biological quality in a hybrid offspring. The adjective derived from heterosis is heterotic....

, sex-links can be extremely good egg-layers which often produce 300 eggs a year or more depending on the quality of care and feed.

Two common varieties are the Black sex-link (also called Black Stars) and the Red sex-link (also called Red Stars). Blacks are a cross between a Rhode Island Red

Rhode Island Red

The Rhode Island Red is a breed of chicken . They are a utility bird, raised for meat and eggs, and also as show birds. They are a popular choice for backyard flocks because of their egg laying abilities and hardiness. Non-industrial strains of the Rhode Island Red are listed as recovering by the...

 or New Hampshire

New Hampshire (chicken)

The New Hampshire breed of chicken originated in the state of New Hampshire in the United States. Poultry farmers, starting with Rhode Island Reds and performing generation after generation of selective breeding, intensified the characteristics of early maturity, rapid full feathering, and...

 rooster and a Barred Rock hen. Red sex-links are a cross between a Rhode Island Red or New Hampshire rooster and a White Rock, Silver Laced Wyandotte

Wyandotte (chicken)

The Wyandotte is a breed of chicken originating in the United States. The first examples of the breed appeared in 1870s. Wyandottes are a docile, dual-purpose breed kept for their brown eggs and for meat. They appear in a wide variety of color patterns, and are popular show birds. The Wyandotte...

, Rhode Island White or Delaware

Delaware (chicken)

The Delaware is a breed of chicken originating in the U.S. state of Delaware. It was once of relative importance to the U.S. chicken industry, but today is critically endangered. It is primarily suited to meat production but also lays reasonably well...

 hen. One example of a red linked breed is the Red Shaver

Red Shaver

The Red Shaver is a sex linked breed of chicken developed in Canada. Pullets are reddish-brown in colour with white underfeathers, while males are white with a few red markings on the feathers. It is a hardy, dual-purpose breed laying brown eggs and dressing out between three and five pounds. They...

. In Europe, the Cream Legbar

Cream Legbar

The Cream Legbar is an autosexing type of chicken. This means that you can tell the sex of the chick at hatch, and they breed true. The Cream Legbar originated as a cross between Brown Leghorns and Barred Rock with some Araucana blood in them. This is reflected in the crest and the blue eggs that...

 (an actual true-breeding pure breed) and ISA Brown

ISA Brown

The ISA Brown is a hybrid type of Sex Link chicken, which is the result of crossing Rhode Island Reds and Rhode Island Whites. The ISA Brown is a hybrid, not a true breed...

sex-links also exist.