Q.87 To which class of Drosophila developmental genes does fushi tarazu (ftz) belong?
(A) Gap genes
(B) Segment polarity genes
(C) Pair rule genes
(D) Maternal effect genes
Fushi tarazu (ftz) belongs to the pair-rule genes class in Drosophila developmental segmentation.
This gene is expressed in seven stripes at the blastoderm stage, defining even-numbered parasegments during embryogenesis.
The correct answer is (C) Pair rule genes.
Option Analysis
Gap genes establish broad regions along the anterior-posterior axis, responding to maternal morphogen gradients like bicoid and nanos; examples include hunchback, Krüppel, and knirps, with mutations deleting large contiguous body sections. Ftz does not fit, as its striped pattern refines rather than defines broad domains.
Segment polarity genes operate within each segment to set anterior-posterior polarity and boundaries; examples include wingless, hedgehog, and engrailed, regulated by pair-rule genes like ftz. Ftz activates these but is upstream.
Pair rule genes divide the embryo into pairs of segments via periodic stripes (seven per gene); ftz exemplifies this, encoding a homeodomain protein essential for even parasegments, with mutants lacking alternate segments.
Maternal effect genes provide anterior-posterior polarity via egg gradients (e.g., bicoid, nanos); mutations affect all progeny regardless of zygotic genotype. Ftz is zygotic, not maternal.
Drosophila Segmentation Hierarchy
Maternal genes initiate polarity, activating gap genes in broad bands. Gap genes then trigger pair-rule genes like ftz, hairy, and even-skipped in 14 parasegment primordia. Pair-rule genes refine into segment polarity genes for final patterning, culminating in homeotic identity.
Fushi tarazu (ftz), a cornerstone of fushi tarazu ftz Drosophila pair rule genes, drives embryonic segmentation in Drosophila melanogaster. This pair-rule gene expresses in seven blastoderm stripes, defining even-numbered parasegments and regulating downstream targets like segment polarity and homeotic genes. For CSIR NET aspirants, mastering ftz classification reveals the hierarchy of Drosophila developmental genes.
Pair-Rule Gene Role
Ftz encodes a homeodomain transcription factor activated by gap genes, forming stripes via zebra and autoregulatory enhancers. Mutants lack alternate segments, confirming its periodic patterning function. Unlike broad gap domains, ftz achieves frequency doubling for 14 parasegments.
Distinction from Other Classes
| Gene Class | Expression Pattern | Key Examples | Mutation Phenotype | Relation to ftz |
|---|---|---|---|---|
| Gap genes | Broad bands | hunchback, Krüppel, knirps | Large gaps | Upstream activators of ftz |
| Segment polarity | Intra-segment stripes | wingless, hedgehog | Segment polarity defects | Downstream targets of ftz |
| Pair-rule | 7 stripes (ftz even) | ftz, even-skipped, hairy | Paired segment deletions | ftz class |
| Maternal effect | Gradients in egg | bicoid, nanos | Polarity loss in progeny | Initiate cascade to ftz |
This table highlights ftz’s unique pair-rule position.
Exam Relevance
In CSIR NET Life Sciences, questions test fushi tarazu ftz Drosophila pair rule genes hierarchy: maternal → gap → pair-rule → segment polarity. Ftz’s stripe-specific role underscores zygotic refinement post-maternal cues.
