Hemoglobin FAS refers to the specific hemoglobin phenotype found in infants who have the sickle cell trait.
Understanding Hemoglobin FAS
- Sickle Cell Trait: This condition occurs when an individual inherits one gene for normal hemoglobin (hemoglobin A) and one gene for sickle cell hemoglobin (hemoglobin S).
- Infant vs. Adult: Interestingly, the phenotype differs slightly depending on age. In infants, this trait is characterized by hemoglobin FAS, while in adults, it's typically referred to as hemoglobin AS. This difference is primarily due to the presence of fetal hemoglobin (HbF) in infants which diminishes after birth.
- Phenotype: The term "phenotype" refers to the observable characteristics of an organism as a result of the interaction of the genotype with the environment. In this case, the specific combination of hemoglobin types (F, A, and S) leads to the observed characteristic at different ages.
- Inheritance: To have hemoglobin FAS or AS, one parent must have the sickle cell trait, while the other parent can have normal hemoglobin (AA).
Hemoglobin FAS vs. Hemoglobin AS
| Feature | Hemoglobin FAS (Infants) | Hemoglobin AS (Adults) |
|---|---|---|
| Age | Typically found in infants | Typically found in adults |
| Hemoglobin | Mix of F, A, and S | Mix of A and S |
| Association | Linked to sickle cell trait in early life | Linked to sickle cell trait |
Key Takeaways
- Hemoglobin FAS is a phenotype related to the sickle cell trait observed in infants due to the presence of fetal hemoglobin.
- It is the result of inheriting one hemoglobin A gene and one hemoglobin S gene.
- The phenotype transitions to hemoglobin AS in adulthood as the levels of fetal hemoglobin decline.
