Final answer:
The probability of a person having an autosomal recessive disease when his or her parents are unrelated is very low, approximately 0.1%.
Step-by-step explanation:
The probability of a person having an autosomal recessive disease when his or her parents are unrelated can be calculated using the Hardy-Weinberg equation. Given that the frequency of the disease-causing allele is 0.03, we can assume the frequency of the recessive allele (q) is 0.03 and the frequency of the dominant allele (p) is 0.97 (since p + q = 1).
The probability of a person being a carrier of the disease-causing allele (2pq) would be 2 x 0.03 x (1 - 0.03) = 0.0558, which is approximately 0.056. This means that the probability of a person being homozygous recessive and having the disease (q²) would be 0.03 x 0.03 = 0.0009, which is approximately 0.001 (0.1%).
Therefore, the probability of a person having the disease when his or her parents are unrelated is very low, approximately 0.1%.