Final answer:
The essential requirement for population-based newborn screening is that interventions for the disorder are available, allowing for treatment or management of the condition detected. The correct option is B.
Step-by-step explanation:
A key requirement for population-based newborn screening is that interventions for the disorder are available. This means that there must be measures that can be taken to treat, manage, or prevent the health issues associated with the detected disorder should a positive test result occur.
While knowing the gene responsible and understanding the disease alleles are important for diagnosis and screening, the availability of interventions is critical for justifying the inclusion of a particular disorder in a newborn screening program.
It's not essential that the disorder be associated with few different disease alleles or have no family history to be included in the screening; such characteristics don't negate the value of early detection and intervention.