Q.101 In Drosophila, mutations in homeotic genes result in which one of the following developmental
defects?
(A) The anterior portion of the embryo will not develop
(B) Several segments in the anterior region of the embryo will be lost
(C) Segmentation will be lost, and the embryo will have only one segment
(D) Segment-specific identities will be lost

Homeotic gene mutations in Drosophila cause homeotic transformations where one body segment develops the identity of another, rather than failing to form segments. This is a classic developmental biology concept tested in GATE Life Sciences.

Option Analysis

(A) The anterior portion of the embryo will not develop
Incorrect. Anterior development depends on maternal effect and gap genes (e.g., bicoid, hunchback); homeotic genes act later to specify segment identity.

(B) Several segments in the anterior region of the embryo will be lost
Incorrect. Segment loss results from pair-rule or segment polarity gene mutations (e.g., even-skipped deletes odd segments); homeotics preserve segment number.

(C) Segmentation will be lost, and the embryo will have only one segment
Incorrect. Segmentation genes (gap, pair-rule, segment polarity) establish the 14 segments; homeotic (Hox) genes assign identities like haltere vs. wing.

(D) Segment-specific identities will be lost
Correct. Mutations like Antennapedia (antenna → leg) or Ultrabithorax (haltere → wing) transform one segment’s structures to another’s, without altering segment count or polarity.

Homeotic Gene Function

Homeotic genes (Antp, Ubx, Scr in bithorax/Antp complexes) are Hox cluster transcription factors expressed in parasegments along A-P axis. Loss-of-function leads to anterior transformations (e.g., Ubx mutant: abdominal → thoracic); gain-of-function posteriorizes (e.g., Antp in head).

Drosophila homeotic genes mutations developmental defects transform segment identities (e.g., legs replace antennae), highlighting Hox code precision in embryogenesis.