Question

Thalassemia is an inherited anemic disorder in humans. Affected individuals exhibit either a minor anemia or a major anemia. Assuming that only a single gene pair and two alleles are involved in the inheritance of these conditions, is thalassemia a dominant or recessive disorder?

Short answer

Answer: Thalassemia is a recessive disorder.

Step-by-step solution

Understand the context of dominant and recessive traits

Dominant traits are those that are expressed when an organism has at least one dominant allele in its genotype. In other words, whether an individual carries one or two copies of the dominant allele, the trait will be present. On the other hand, a recessive trait is only expressed when an organism has two copies of the recessive allele in its genotype. If an individual carries only one copy of the recessive allele and one copy of the dominant allele, the dominant trait is expressed.

Analyze the inheritance patterns in thalassemia

Thalassemia presents itself in two forms: minor anemia and major anemia. We can assume that major anemia is the more severe, expressed form of the disorder, and minor anemia is the less severe, partially affected state.

Compare the inheritance patterns to dominant and recessive traits

Since there are individuals exhibiting two different expressions of anemia (major and minor), it is likely that these represent heterozygous and homozygous genotypes for the responsible allele. If thalassemia were a dominant disorder, we would expect both affected individuals carrying one copy (heterozygous) and those carrying two copies (homozygous) of the dominant allele to exhibit major anemia. However, this is not observed. Instead, individuals with minor anemia likely carry only one copy of the responsible allele, while those with major anemia inherit two copies. This pattern of inheritance is consistent with a recessive trait, where only those with two copies of the recessive allele exhibit the fully affected state.

Conclusion

Based on the inheritance patterns observed in thalassemia, it is more likely that thalassemia is a recessive disorder, as individuals with one copy of the responsible allele express minor anemia, while those with two copies exhibit major anemia.