Kat C.
asked • 02/26/21Pedigree - Autosomal recessive and dominant
There's a pedigree with an affected mother and unaffected father. They have 6 children, 3 are unaffected and 3 are affected. One of the affected children marries an unaffected person. They have 6 children as well, 3 are affected and 3 are unaffected.
The answer key says this is autosomal dominant but I don't quite understand why it can't be autosomal recessive. Thanks!
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1 Expert Answer
In the family pedigree described, the likeliest scenario is that the mutation is autosomal dominant.
It is possible for a recessive mutation to produce a pedigree like this, but only if both of the unaffected partners are heterozygous carriers, namely, the father-in-law and the child-in-law. This would be an unlikely coincidence, especially if the condition is rare.
In general, if a genetics problem describes a condition as “rare,” you can assume that the unrelated partners are not carriers. This problem did not specify “rare,” but still, it is less likely for the unaffected partner and his/her unaffected father-in-law to both be carriers.
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Daniel H.
Hello Kat. Does the question list that six children are male or female. An easy way to think about this is that for autosomal dominant disorders, if a son inherits the faulty X, that's it. That's an affected individual, but if a daughter inherits a faulty X, she could also inherit one healthy X from dad and still would be affected. In this way, a female could be a heterozygous affected individual or a homozygous affected individual. If the disorder is autosomal recessive, a son could inherit one X and be affected. A daughter however, could inherit one faulty X from affected dad, and a healthy X from her unaffected mom, and be healthy. The sex of the children are an important factor in following these disorders. If the sex is not listed, we could assume that for this problem that the father had one healthy X, and the mother could have one or both faulty X's. The children, if male, would have a 50/50 chance of receiving a faulty X from mom if she were heterozygous, or a 100% chance if she were homozygous. Daughters have just a 50/50 chance of inheriting that faulty X. The point of this is, is that when you get down to it, an autosomal dominant disorder will show up in every generation, and that's what we are seeing in this problem.02/28/21