If a child has the HLA-B27 marker and one parent has been shown not to have it then yes, the other parent must be positive for it. It should be noted however that most people that are HLA-B27 positive never develop any diseases associated with the gene, so it is possible to have it and never know about it.
What is meant by a gene skipping a generation is that it is actually there in the genome of the "skipped" individual but silent, that is, it´s effect cannot be seen. As mentioned above this is most often the case with HLA-B27. This individual´s child might then inherit the gene and be affected by it. A child cannot inherit a gene straight from a grandparent. A parent must have it in his or her own genome in order to pass it on to the next generation.
My husband has the hlab27 marker and has aynkliosingspondilitis (sorry about the spelling) and his parents do not have the diseases associated with the hlab27 marker. I don't believe they have been tested for the marker though. But his great grandfather had AS.
The Content on this Site is presented in a summary fashion, and is intended to be used for educational and entertainment purposes only. It is not intended to be and should not be interpreted as medical advice or a diagnosis of any health or fitness problem, condition or disease; or a recommendation for a specific test, doctor, care provider, procedure, treatment plan, product, or course of action. MedHelp is not a medical or healthcare provider and your use of this Site does not create a doctor / patient relationship. We disclaim all responsibility for the professional qualifications and licensing of, and services provided by, any physician or other health providers posting on or otherwise referred to on this Site and/or any Third Party Site. Never disregard the medical advice of your physician or health professional, or delay in seeking such advice, because of something you read on this Site. We offer this Site AS IS and without any warranties. By using this Site you agree to the following Terms and Conditions. If you think you may have a medical emergency, call your physician or 911 immediately.