A family tree is shown - HSC - SSCE Biology - Question 18 - 2013 - Paper 1

To determine what the family tree represents, we need to analyze the patterns of inheritance visible in the diagram.

1. Examine the Symbols: The tree uses squares for males and circles for females, indicating the presence or absence of a trait. Males and females with the trait are clearly marked.

2. Check for Patterns of Inheritance: Inheritance can be categorized based on dominant and recessive traits or sex-linked traits. A dominant trait typically appears in every generation and is passed from parents to offspring.

3. Analyze Family Transmission: In this family tree, it can be observed that the trait appears in every generation, suggesting that it is likely a dominant trait. In contrast, if it were recessive, it might skip generations.

4. Eliminate Other Options:

   • Sex-linked inheritance often shows a skewed ratio between males and females, which isn't clearly evident here.
   • Co-dominant inheritance would also show mixed traits, typically affecting the phenotype of the offspring in more complex ways.
   • Recessive traits would not appear in every generation, making option (C) less likely.

Given this analysis, the most plausible answer is the Inheritance of a dominant trait.