The pedigree below represents a family of rabbits - VCE - SSCE Biology - Question 4 - 2007 - Paper 1

To determine the mode of inheritance of the disease in question, we can analyze the offspring produced by rabbits II-1 and II-2.

Generational Observation:

1. From generation II, rabbit II-1 is a female that is shaded, indicating that it has the disease. Rabbit II-2 is a male, and since males have one X chromosome, if he had the disease, all his daughters would be affected.

2. In generation III, the offspring of II-1 and II-2 demonstrate a pattern: every daughter of II-1 (who is affected) shows that they are also shaded, meaning they exhibit the disease. This supports the idea that the trait is inherited in a manner consistent with X-linked dominance.

3. Importantly, there are no unaffected male offspring of II-2 that could carry the trait without expressing it, as male rabbits have only one X chromosome. Thus, if the male offspring are shaded, that indicates they inherited the condition as well.

4. The consistent appearance of the disease in the female offspring suggests an X-linked dominant inheritance pattern; affected females transmit the trait to all their daughters, and if a father carries the trait, all daughters will also show the disease because they inherit the X chromosome from him.

Conclusion: The observations from both generations II and III indicate a strong correlation to the X-linked dominant inheritance of the disease.