Ed Lewis won a Nobel Prize in 1995 for discovering homeobox (Hox) genes in the f

Question

Ed Lewis won a Nobel Prize in 1995 for discovering homeobox (Hox) genes in the fly based on mutations that altered segment identity. Antennapedia and Bithorax are two complexes of Hox genes located on Chromosome III of the Drosophila genome.

A. Explain the term “co-linearity” and its importance. (2 marks)

B. Ultrabithorax controls identity in parasegments 5 and 6 (T3). Explain why a loss-of-function mutation in Ubx will cause a T3 segment to develop as a T2.

C. Predict what phenotype would occur if Antennapedia were misexpressed in the fly abdomen. Explain your reasoning.

Explanation / Answer

A) Colinearity is the arrangement of a sequence in the same linear order as another sequence.

Colinearity in developmental genetics is the arrangement of genes in the same order as they are activated along the body axis during development.

B) Loss-of-function mutation in Ubx will cause a T3 segment to develop as a T2. Reason for this comes from temporal differences in the spatial distribution of Ultrabithorax. In earlier development, Ubx is expressed in the abdomen but not the thorax. At this point in time Ubx prevents Dll expression in A1. At later point of time, Dll becomes auto regulatory, and Ubx is no longer capable of preventing appendage formation in T3. Thus Ubx expression in T3 occurs yet it causes these appendages to be altered from the ones that form in T2.

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