Final answer:
Positional cloning is useful for identifying disease genes when the pathogenesis is poorly understood, no candidate genes are obvious, chromosomal rearrangements point to particular genomic regions, and when multiple alleles are involved in the disease, essentially encompassing all the mentioned scenarios.
Step-by-step explanation:
The situations that would support the use of positional cloning for disease gene identification are as follows:
- Disease pathogenesis is poorly understood.
- Candidate genes are not apparent.
- Chromosomal rearrangements highlight regions of interest.
- Many disease alleles can be present in the disease gene.
- All of the above situations would support the use of positional cloning.
Positional cloning can be a beneficial technique in scenarios where the biological mechanisms behind a disease are not well characterized. It is also helpful when there are no clear candidate genes to investigate. The identification of chromosomal rearrangements can indicate specific regions of the genome that may harbor disease-causing genes. Additionally, positional cloning comes into play when multiple alleles can contribute to disease, necessitating the search for the precise genetic variant causing the condition. In essence, all the listed scenarios are situations where positional cloning could aid in identifying disease genes.