Genetics Pullet or Cockerel?

Autosexing Chickens

No matter what Facebook chicken group I’m scrolling through one of the most common posts is “What Sex Is My Bird?”  The website Backyard Chickens has over 107k threads and more than a million posts on the subject. Clearly, sexing chickens isn’t as easy as you’d think. Of course, we can all wait till our bird either crows or lays an egg, but for many of us we’d like, or need, to have that information a lot sooner.

There are a number of ways to figure out the sex of your bird, each with its own merits and limitations. No matter what your method, you really need to understand the reasons why and when they’ll work – and when they won’t. For instance, lots of folks think that feather sexing – looking at the length of primary and secondary wing feathers in chicks – is reliable, but don’t realize that you need to know if the parent stock were either slow or fast feathering. Without that knowledge you’re just guessing.

In this post I’ll explore one reliable method for determining the sex of your birds: autosexing. If you’re not sure what that means, it simply refers to pure breeds in which cockerels and pullets appear different at hatch. It could be as simple as a head spot or different colouring.

If your high school genetics is a bit rusty you can check out this post, but I’ll try to give you the condensed version of a complex theory.

In the 1920s, Cambridge University professor Dr Reginald Punnett used the study of genetics to predict the sex of chickens. He discovered a sex linkage between gold males and silver females. If you breed a Rhode Island Red rooster (gold) and a Light Sussex hen (silver) all their pullets will be darker gold and the cockerels a pale yellow.

Punnett later identified a sex-linked barred (striped) feather pattern: in Plymouth Barred Rocks all the chicks are black with white spots on their heads. Cockerels are lighter in colour with irregular and elongated head spots. Darker pullets have more round, compact head spots.

During the 1920’s and 30’s Punnett and his team worked on a number of autosexing breeds using the barred feather gene as the basis of their program.

In purebred barred birds, females receive one copy of the barred gene (from their father) which lightens their down slightly. Males receive two barred genes (one from each parent), creating even lighter down and more barring. Using the barring gene in combination with certain background colors, autosexing breeds were created from a cross between a barred breed and a wild type or brown breed.

He experimented with brown coloured roosters bred to silver females who produced chicks that also could be sexed at hatch. Males were silvery with a head spot, while females had ‘chipmunk stripes’ down their back.

After further experimentation he developed the Legbar: a combination of Danish Brown Leghorn (good egg production), Barred Plymouth Rock (barred gene) and the Araucana (a South American crested, blue egg layer). The result was a crested, blue egg layer with good egg production and the barred gene. After almost a further two decades of tweaking, the Legbar was a genetically stable breed.


If Punnett’s name sounds familiar that’s maybe because you’ve heard of the Punnett square:  a graphical way to calculate and depict all the combinations and frequencies of the different genotypes (genetics) and phenotypes (appearance) among the offspring of a cross according to Mendelian genetics.


The development of autosexing became more popular in Europe than in North America that relied on sex-linked breeds. The former took more time to develop and had lower egg production than hybrids that could also easily be sexed as chicks.

Auto-sexing birds will breed true, generation after generation, and are considered purebreds. Sex-linked birds are the first generation hybrids of two different pure breeds. Sex-linked birds bred together aren’t able to produce sex-linked offspring.

Buying autosexing birds is a simple, reliable way to determine the sex of your purebred chicks at hatch. If you are producing a cross then you need to understand what genetics each parent carries and how they get passed on.

The reason I know that this Crested Cream Legbar cross chick is a cockerel is because he inherited one barred gene from his mother and none from his Appenzeller Spitzhauben x father (who doesn’t carry them).  Hens pass the barred gene on to their sons and not their daughters. He was also born with the classic large, elongated white head dot found in Barred Rock cockerels. (purebred Cream Legbar hen on right; her son, Cream Legbar x cockerel on right)

There are a number of autosexing breeds developed in the UK and Europe. Most of their names are contractions of the original breeding stock names, which is why they sound similar: Amrock, Ancobar, Barnebar, Bielefelder Kennhuhn, Brockbar, Brussbar, Buffbar, Cambar, Cobar, Legbar (Cream and Gold), Dorbar, 55 Flowery Hen, Hambar, Niederrheiner, Norske Jaerhon, Oklabar, Polbar, Rhodebar, Welbar, Whealbar and Wybar.

Many are now threatened or endangered. The Legbar is one of the most popular autosexing birds.

Credits: Greenfire Farms; My Pet Chicken; Poultry World; Scratch Cradle. Featured Image: Backyard Chickens Image Credits: Backyard Chickens; Hub Pages; Patty Penny

I’ll explore the development of sex-linked breeds in a future post.

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