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?

Verified step by step guidance

1. Understand the phenotypes associated with the disorder: Thalassemia shows two types of anemia—minor and major—indicating different severity levels in affected individuals.
2. Recall the definitions of dominant and recessive inheritance: A dominant disorder typically shows the trait in heterozygous individuals, while a recessive disorder requires two copies of the mutant allele to express the trait.
3. Consider the genotype-phenotype relationship: In thalassemia, individuals with one mutant allele (heterozygotes) usually have minor anemia, while those with two mutant alleles (homozygotes) have major anemia.
4. Analyze the inheritance pattern: Since heterozygotes show a milder form of the disease and homozygotes show a more severe form, the mutant allele is expressed in both heterozygous and homozygous states but with different severity.
5. Conclude the mode of inheritance: This pattern suggests that thalassemia is inherited as an incompletely dominant or codominant disorder rather than strictly dominant or recessive.

Key Concepts

Mendelian Inheritance and Alleles

Mendelian inheritance involves traits controlled by single gene pairs with dominant and recessive alleles. Dominant alleles express the trait when present in one or two copies, while recessive alleles require two copies to show the trait. Understanding this helps determine how thalassemia traits are passed and expressed.

Dominant vs. Recessive Genetic Disorders

Dominant disorders manifest when at least one dominant allele is present, often causing symptoms in heterozygotes. Recessive disorders require two copies of the recessive allele for symptoms to appear, with carriers typically unaffected or mildly affected. This distinction is key to classifying thalassemia based on symptom severity in heterozygotes and homozygotes.

Phenotypic Expression of Thalassemia

Thalassemia shows variable severity: minor anemia in heterozygotes and major anemia in homozygotes. This pattern suggests incomplete dominance or recessive inheritance with partial expression in carriers. Recognizing this helps infer whether thalassemia behaves as a dominant or recessive disorder.