Correct option is A
The correct answer is (a). The ultrabithorax (Ubx) gene is a homeotic selector gene that plays a critical role in specifying the identity of the third thoracic segment in Drosophila. If the Ubx gene is deleted or inactivated, the third thoracic segment (which normally develops halteres) is transformed into a segment with the characteristics of the second thoracic segment, leading to the formation of four wings instead of the normal two. This is due to the fact that the second thoracic segment carries the wing identity, and the loss of Ubx causes the third segment to adopt a similar identity.
Information Booster
- This phenomenon demonstrates the role of homeotic genes in segment identity and how a single gene can influence the morphological outcome of a segment.
- Halteres are modified wings that function in balance and are typically found in the third thoracic segment. When Ubx is deleted, this segment fails to develop halteres and instead develops wings.
- The loss of Ubx in the third thoracic segment results in the transformation of halteres to wings, which can lead to developmental abnormalities, such as extra wings.
Additional Information
- Option (b): The third thoracic segment develops halteres is incorrect because in the absence of the ultrabithorax gene, the third thoracic segment will no longer develop halteres but will instead develop wings, as described in the correct answer.
- Option (c): The second thoracic segment loses wings is incorrect because the second thoracic segment retains its identity in this scenario, and only the third thoracic segment is affected by the loss of Ubx.
- Option (d): The first and second thoracic segments fuse and wings are formed on the third thoracic segment is incorrect as well because this is not the typical outcome when ultrabithorax is deleted. Only the third segment transforms into the second segment's identity, leading to extra wings on the third thoracic segment, not fusion between the first and second thoracic segments.
