Question

1.4.2 test (cst): heredity
question 15 of 25
what kind of trait is illustrated in the diagram?
legend
a. autosomal recessive
b. autosomal dominant
c. sex - linked dominant
d. sex - linked recessive

Explanation:

Step1: Analyze autosomal recessive traits

Autosomal recessive traits often skip generations. In the pedigree, there are affected individuals whose parents are unaffected (e.g., in the second - generation parents (unaffected) having an affected child in the third generation).

Step2: Rule out autosomal dominant

Autosomal dominant traits do not skip generations. If it were autosomal dominant, at least one parent of an affected child would be affected (since the trait is dominant). But here, we see unaffected parents having affected children.

Step3: Rule out sex - linked dominant

For sex - linked dominant, affected fathers would pass the trait to all daughters (because daughters get the father's X - chromosome). But in the given pedigree, this pattern is not observed.

Step4: Rule out sex - linked recessive

In sex - linked recessive, if a mother is unaffected (carrier) and father is unaffected, sons have a 50% chance of being affected. But in autosomal recessive, both males and females can be affected in a more “random” pattern among siblings (not following strict X - linked inheritance patterns like criss - cross inheritance which is more typical for sex - linked recessive). The skipping of generations and the pattern of affected individuals from unaffected parents is more consistent with autosomal recessive.

Answer:

A. Autosomal recessive