Inherited Disease

Dr. Foster: ‘All right, everyone. Let’s gather around this bench for the next part of today’s lab discussion. I’d like to bridge our focus from Mendelian peas to real-life genetic disorders.’ 

Just as we start reviewing new data, Eleonore, a first-year medical student, stops by the lab to observe our session. She’s curious about a particular scenario involving a family with a history of thalassemia. Eleonore explains that her husband ‘Jake’ is a carrier for this recessive condition and wonders about the likelihood of passing the disorder on to any children they might have.

You: ‘What is thalassemia?’

Eleonore: ‘Thalassemia is a group of inherited blood disorders affecting hemoglobin production, often caused by recessive genetic variants. Individuals who carry one defective allele typically show no symptoms (carriers), while those with two copies of the defective allele experience reduced hemoglobin levels and symptoms such as anemia. Early detection and genetic counseling are vital so families can better plan for healthcare and management of the condition. So I could really use your help.’

To address Eleonore’s question, we first need to clarify what ‘carrier’ means. Here are two possible definitions—tell me which you think is correct:

Definition 1:
The individual has a single copy of the disease-causing gene and therefore shows symptoms of the disease.

Definition 2:
The individual has a single copy of the disease-causing gene but does not show any symptoms.