The Red Sex link is a hybrid meaning that they are not a breed of chicken and cannot produce a red sex link by crossing both of those breeds together. This usually makes the Red Sex Links useless for breeding since they can't produce another purebred. However, two purebreds were originally crossed to make this breed which was the Rhode Island Red male and White Leghorn female. Today, in order to produce a Red Sex Link The Rhode Island Red male can either be crossed by the White Plymouth Rock female, Rhode Island White Female or the Delaware female. Crossing them with these different breeds will probably cause the offspring to result in different temperaments though. This chicken is not recognized by the "American Poultry Association".
Pic above by @MamaDoolittle
Red Sex Links can be sexed at day of hatch and the males and females are a completely different color even as they develop later into maturity. As baby chicks, the males are more white while the females are red. The Red Sex Link is very popular and well known chicken kept by a lot of chicken owners and and were purposely bred for high egg production. According to a lot of our Backyard Chicken members, Red Sex links are lucky to even live past 2 to 3 years because of their high egg production and large eggs causes problems such as prolapse of the uterus or egg bound. This also causes a calcium deficiency which is why they lay soft shelled eggs later in life. Red Sex Links also come in to maturity earlier than other chicken breeds which could be another probable cause of these chickens being short lived.
Red Sex Link chicks showing the comparison of color in the males and females.
Males white. Females red.
Red Sex Links are usually the most friendly in the chicken world, are fun to have around and most easily tamed. The hens are never skittish, they follow you around and sit on your lap like pets. According to a some of our Backyard Chicken members, including myself, There has also been a lot of aggression towards humans in some lines of Red Sex Links. They are rough and rugged and can be very bossy with some breeds. This trait in Red Sex Links might of very well been acquired by the Rhode Island Red who have also been known sometimes to be aggressive. Here is a pic of a Red Sex Link pullet about 10 seconds prior to attacking owner.
Different Red Sex Link Hen first being socialized. Easily tamed and friendly.
Some Red Sex Links feathers change color overtime starting at a really red color prior to molting. As molting takes place, new feathers usually come in more brown. Here is a picture for comparison.
After: Same chicken.
There are different names for Red Sex Links even though they are the same exact breed. Hatcheries and chicken farms will use different names for Red Sex Links. Here is a list below.
Gold Sex Link
This is probably not a comprehensive article but does provide all the basic information.