MCAT® ExamBiological and Biochemical Foundations of Living SystemsMedium
A geneticist is studying a family pedigree for a rare genetic disorder. They observe that affected individuals appear in every generation, and every affected person has at least one affected parent. Furthermore, the disorder affects both males and females equally. What is the most likely mode of inheritance for this disorder?
- AAutosomal recessive
- BX-linked recessive
- CMitochondrial inheritance
- DAutosomal dominant
Show answer & explanationAnswer & explanation
Correct answer: D. Autosomal dominant
The pattern of affected individuals in every generation, affected offspring having at least one affected parent, and equal incidence in males and females are classic hallmarks of autosomal dominant inheritance. A single copy of the mutated allele is sufficient to cause the disorder.
Why the other options are wrong
- A. Autosomal recessive disorders often skip generations and affected individuals usually have unaffected parents.
- B. X-linked recessive disorders typically affect males more frequently and do not show male-to-male transmission.
- C. Mitochondrial inheritance is passed only from mother to all offspring, and typically affects all children of an affected mother.
Autosomal Dominant Inheritance
A pattern of inheritance where an affected individual has one copy of a mutated gene and one normal gene on a non-sex chromosome (autosome). The mutated gene is dominant, meaning only one copy is needed to express the trait.
- Affected individuals in every generation (vertical transmission).
- Affected offspring have at least one affected parent.
- Males and females are affected equally.
- Affected individuals have a 50% chance of passing the allele to each child.
Memory trick: Dominant: Dad or Mom, always showing up.