USA Biology Olympiad (USABO) Practice Exam

In the context of inheritance patterns represented in a pedigree, what could be possible modes of inheritance?

1. Autosomal dominant only

2. Autosomal recessive or X-linked recessive only

3. X-linked dominant only

4. Both II or IV only

The correct answer is: Both II or IV only

In the context of a pedigree analysis for understanding inheritance patterns, it is important to recognize that there are several modes of inheritance that can be observed beyond just a single type. The correct answer highlights the possibility of having multiple modes of inheritance, specifically focusing on the variety that can be observed within a pedigree. Pedigrees can show traits that follow different inheritance patterns, including autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive. When analyzing a pedigree, it is crucial to consider all possible modes of inheritance to accurately interpret how traits are passed from one generation to the next. The answer indicates that both autosomal recessive and X-linked recessive traits can coexist within one pedigree. This means that individuals showing a trait could inherit it through one of these two mechanisms. Autosomal recessive traits require two copies of the recessive allele for the phenotype to be expressed, while X-linked recessive traits only require one copy in males (who have one X chromosome). Having a broader understanding of inheritance patterns allows for better predictions and understanding of genetic disorders and traits within families, and recognizing that both mentioned types can appear in a pedigree is foundational for genetics. Therefore, interpreting pedigrees involves considering that multiple inheritance patterns can inform