What does "Obligatory Carrier" mean in genetics?

Answers:
Simply put: Obligatory carriers are of normal phenotype but have a parent that has a particular recessive disease that they carry and therefore are at risk of passing the trait on to their offspring.
More comprehensively put: Obligatory carrier is usually referred to in recessive diseases. It means that the person MUST be a carrier of a particular trait. For example hemophilia is a sex-linked recessive disease. If a man is born with hemophilia, all of his daughters automatically have to be carriers of the disease. This is because they have to get the X with the trait on it from their father. Now it is up to the mother whether the daughter will have hemophilia. If the mother is a carrier there is a 50/50 chance that the daughter will be a carrier or have the disease. If the mother is homozygous dominant then the daughter can only be a carrier. In autosomal recessive disease, if a parent has a recessive disease then all of their children must either carry the trait or have the disease because the parent with the disease can only give that trait to their child. It is up to which allele they get from the normal parent as to whether they have the disease.

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Well, it's been a while since my last genetics course, but as I recall it, it's the offspring of a homozygous recessive individual with another individual. If one parent is homozygous recessive, and the other one homozygous dominant, the offspring will all be carriers of the recessive trait--which is what I recall being the meaning of "obligatory carrier" in the context of genetics.We used to breed 'em in Drosophila melanogaster for the fruit fly labs for students, years ago. We'd cross a strain that was homozygous redeyed with homozygous whiteyed, and then let the students try to figure out what was going on. The obligatory carriers would, when back-crossed, produce 1/4 homozygous dominant, 1/2 heterozygous and 1/4 homozygous recessive.

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