Neshele and Fahim are contemplating having children and visited a genetic counselor. They are concerned because, while both Neshele and Fahim are healthy, they both have Turkish relatives who have suffered from thalassemia.
Thalassemia is a genetic condition caused by mutations in either the gene encoding $\alpha$ globin or the gene encoding $\beta$ globin, components of hemoglobin. Thalassemia is an autosomal recessive disorder, and individuals homozygous for either of these mutations typically suffer from severe anemia and reduced quality of life. Heterozygous individuals may be either asymptomatic or have mild symptoms, but they additionally serve as carriers.
Neshele's father is a known carrier for $\alpha$ thalassemia and has mild symptoms of anemia. However, neither Neshele's mother nor brother has any symptoms. Additionally, a family history shows that no one on Neshele's mother's side of the family has ever had thalassemia or has been a known carrier.
Fahim is the oldest of four siblings. His sister Samira passed away from severe $\alpha$ thalassemia shortly after birth. Neither of Fahim's parents nor his other two siblings has any symptoms of thalassemia.
Based upon this information, the genetic counselor calculated the probability of a child of Neshele and Fahim having severe $\alpha$ thalassemia.
What is this probability?