“Draw a three-generation Arabian horse pedigree for severe combined immunodeficiency (SCID), autosomal recessive: two carrier founders, a carrier mare bred to a carrier stallion, and their foal that died of SCID marked as the proband, with a carrier and a clear sibling.”
看懂背後的決策。
SCID foals die within months, so no affected horse appears as a parent.
The foal is affected because both its dam and sire are carriers, each passing one copy of the recessive allele.
The generation-I founders are both carriers, which explains carrier status in two of their three offspring.
The deceased mark on the proband records the outcome breeders need to see at a glance.
Use this layout to explain a recessive condition in a breeding record. Carrier status should come from a DNA test, and mating decisions belong with a veterinarian.
常見問題
Is Arabian SCID autosomal recessive?
Yes. A foal is affected only when it inherits the allele from both its dam and its sire.
Why are both parents of the affected foal carriers?
Affected foals do not live long enough to breed, so the allele is passed on by healthy carriers. Two carriers have a one-in-four chance of an affected foal with each mating.
Can an unaffected horse be a carrier?
Yes. Carriers are clinically normal; only a DNA test tells a carrier from a clear horse.