How auto-sexing works in breeds like the Cream Legbar explained by @wingandwool on Instagram.

Video is posted with permission from its creators at Wing and Wool's instagram page.
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Wing and Wool's website: https://www.wingandwool.com

"Sex-linked genes are carried on the Z chromosome—one of the sex chromosomes in birds.
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Barring, or the appearance of white bars on an otherwise black feather, is one of those genes.
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In auto-sexing breeds, males (ZZ) will always inherit two copies of barred and be double-barred (meaning they have more white and are LIGHTER in appearance). Females, (ZW) can only inherit one copy of barred, since their W chromosome is smaller than a Z and is missing that gene locus. Females will always be single-barred in such breeds and will thus have less white and appear DARKER!
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Auto-sexing breeds like the Cream Legbar will breed true each generation, producing offspring that can be sexed at hatch based on down color.
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Sex-linked birds, on the other hand, are F1 hybrids of two different breeds (such as my ISA browns) and will not breed true. If you breed two sex-linked birds together, you do not get offspring that are able to be sexed at hatch."