Final answer:
A cis deletion in the context of thalassemia genetics is associated with a higher risk of severe disease in offspring because it leads to a greater imbalance in globin chain synthesis compared to trans deletions.
Step-by-step explanation:
Cis Deletion and Thalassemia
For a gene deletion that is associated with an increased risk of severe thalassemia in offspring, a cis deletion is typically more concerning. With thalassemia, a genetic blood disorder, certain deletions can lead to a reduction in the synthesis of hemoglobin chains. In alpha-thalassemia, for instance, there are two pairs of alpha-globin genes, and the deletion of both genes on the same chromosome (in cis) can lead to more severe outcomes than deletions on different chromosomes (trans). This is because if one chromosome retains both functional genes, some normal hemoglobin can still be produced, whereas with a cis deletion, a greater imbalance in globin chain synthesis occurs. Therefore, the answer is: 1) Cis deletion.