Question

In the following pedigree chart, the mutant trait is shaded black. The gene responsible for the trait is:

• A. dominant and sex-linked
• B. dominant and autosomal
• C. recessive and sex-linked
• D. recessive and autosomal

Hint:

If you see two white (unaffected) parents with a black (affected) child, immediately think "Recessive." If both sons and daughters are affected from unaffected parents, it is almost certainly "Autosomal Recessive."

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Pedigree analysis is used to determine the mode of inheritance of a genetic trait. We look for specific patterns: dominant traits usually appear in every generation, while recessive traits can "skip" generations or appear from unaffected parents. Autosomal vs. Sex-linked depends on the ratio of affected males to females and the transmission between parents and offspring.
Step 2: Detailed Explanation:
1. Recessive vs. Dominant: If two unaffected parents have an affected child, the trait must be recessive. The parents are carriers (heterozygous), and the child has inherited two recessive alleles. 2. Autosomal vs. Sex-linked: If a trait is X-linked recessive, an affected daughter must have an affected father (since she needs two 'x' alleles, one from each parent). If an unaffected father has an affected daughter, the trait cannot be X-linked; it must be autosomal. 3. Observation: In typical charts showing this pattern (unaffected parents producing affected offspring of both sexes), the only logical conclusion is autosomal recessive.
Step 3: Final Answer
The gene responsible is recessive and autosomal.