To solve this problem, we need to identify which condition is caused by an autosome-linked dominant trait. Let's analyze each option:$\newline \bullet$Option 1: Sickle cell anaemia$\newline$ - Sickle cell anaemia is an autosomal recessive disorder caused by a mutation in the hemoglobin-beta gene on chromosome 11.$\newline$ - Therefore, it is not an autosome-linked dominant trait.$\newline \bullet$Option 2: Myotonic dystrophy$\newline$ - Myotonic dystrophy is an autosomal dominant disorder. It is caused by a mutation in the DMPK gene on chromosome 19.$\newline$ - Therefore, it is an autosome-linked dominant trait.$\newline \bullet$Option 3: Haemophilia$\newline$ - Haemophilia is a sex-linked recessive disorder, typically associated with mutations in genes on the X chromosome.$\newline$ - Therefore, it is not an autosome-linked dominant trait.$\newline \bullet$Option 4: Thalassemia$\newline$ - Thalassemia is an autosomal recessive disorder caused by mutations in the genes responsible for hemoglobin production.$\newline$ - Therefore, it is not an autosome-linked dominant trait.$\newline$Based on the analysis, the correct answer is Option 2: Myotonic dystrophy, which is an autosome-linked dominant trait.