Allosomal Recessive Traits

Allosomal recessive traits are genetic disorders that are inherited in an autosomal recessive manner but are located on the sex chromosomes (allosomes). In humans, the sex chromosomes consist of the X and Y chromosomes. Allosomal recessive traits are typically associated with genes located on the X chromosome, as the Y chromosome is much smaller and contains fewer genes.

Mendelian Gene Disorders

Mendelian gene disorders are inherited disorders caused by a single gene mutation. These disorders follow Mendelian inheritance patterns, which include autosomal dominant, autosomal recessive, and X-linked inheritance.

Representative Allosomal Recessive Trait

Among the given options, haemophilia is the representative allosomal recessive trait. Haemophilia is a genetic disorder characterized by the inability of the blood to clot properly, leading to excessive bleeding. It is caused by mutations in the genes responsible for producing clotting factors VIII (haemophilia A) or IX (haemophilia B), which are located on the X chromosome.

Explanation

- Thalassemia: Thalassemia is an autosomal recessive disorder caused by mutations in the genes responsible for producing hemoglobin. It is not an allosomal recessive trait.

- Sickle Cell Anemia: Sickle cell anemia is an autosomal recessive disorder caused by a mutation in the gene that codes for the beta-globin chain of hemoglobin. It is not an allosomal recessive trait.

- Haemophilia: Haemophilia is an allosomal recessive trait caused by mutations in the genes responsible for producing clotting factors VIII or IX. It is inherited in an X-linked recessive manner, meaning it primarily affects males, while females are usually carriers.

- Mytonic Dystrophy: Mytonic dystrophy is an autosomal dominant disorder caused by mutations in the DMPK gene. It is not an allosomal recessive trait.

In conclusion, the allosomal recessive trait among the given options is haemophilia.