Final answer:
Drosophila melanogaster, or fruit fly, was chosen as a model organism for genetic analysis due to its large polytene chromosomes, which facilitate genetic observation and research.
Step-by-step explanation:
The species chosen as a model organism for genetic analysis due to unusually large "polytene" chromosomes is Drosophila melanogaster, commonly known as the fruit fly. These enlarged chromosomes have been very advantageous in genetic research, allowing scientists to easily observe and study chromosomal processes. Drosophila is widely used in genetic studies, including genetic mapping, studying gene function, and understanding patterns of inheritance.