MCDB 4650 Hox Genes and Segment Identity

1. MCDB 4650Hox Genes and Segment Identity

2. What establishes the initial anterior boundary of each Hox gene? a) combinations of gap gene products b) combinations of pair rule gene c) (a) and (b) d) segment polarity gene products e) the boundaries of expression of other Hox gene products

3. Not long after blastoderm cellularization, the egg-polarity, gap, and pair-rule genes are no longer expressed and their gene products disappear. In the absence of some other control mechanism, what do you predict would happen to Hox gene expression in this situation? A) Hox gene expression would shut down. B) Anterior boundaries of Hox gene expression would move anteriorly. C) Anterior boundaries of Hox gene expression would move posteriorly. D) The most posterior Hox gene would eventually repress expression of all the others. E) The most anterior Hox gene would eventually repress all the others.

4. Which one of the following classes of Drosophila genes does not play any role in the physical process of segmentation along the A-P axis? a) egg polarity genes b) gap genes c) pair-rule genes d) segment polarity genes e) Hox genes

5. Which one of the following classes of Drosophila genes does not play any role in determining the identities of different elements along the A-P axis? a) egg polarity genes b) gap genes c) pair-rule genes d) segment polarity genes e) Hox genes

6. . . . Scr Antp Ubx AbdA AbdB Expressed in: T1 T2 T3 A1-A5 A6-A8 Bithorax complex Antennapedia complex The diagram below shows a simplified diagram of the Drosophila complex of Hox genes and where these Hox genes are expressed in the segments of the embryo (T1-A8). A homeotic mutant fly exhibits a transformation in which the T3 segment has taken on the characteristics of the T2 segment. What type of transformation has the altered segment undergone? i) Anterior to posterior ii) Posterior to anterior

7. . . . Scr Antp Ubx AbdA AbdB Expressed in: T1 T2 T3 A1-A5 A6-A8 Bithorax complex Antennapedia complex The diagram below shows a simplified diagram of the Drosophila complex of Hox genes and where these Hox genes are expressed in the segments of the embryo (T1-A8). A homeotic mutant fly exhibits a transformation in which the T3 segment has taken on the characteristics of the T2 segment. What type of mutation in a Hox gene is likely to have caused this transformation? i) dominant gf ii) recessive lf

8. . . . Scr Antp Ubx AbdA AbdB Expressed in: T1 T2 T3 A1-A5 A6-A8 Bithorax complex Antennapedia complex The diagram below shows a simplified diagram of the Drosophila complex of Hox genes and where these Hox genes are expressed in the segments of the embryo (T1-A8). A homeotic mutant fly exhibits a transformation in which the T3 segment has taken on the characteristics of the T2 segment. Which Hox gene is likely to be mutated? i) Scr ii) Antp iii) Ubx iv) AbdA

9. . . . Scr Antp Ubx AbdA AbdB Expressed in: T1 T2 T3 A1-A5 A6-A8 Bithorax complex Antennapedia complex You have isolated a large deletion mutation that has lost the entire Bithorax complex. Embryos homozygous for the deletion die as first instar larvae, but segments can be identified from the denticle belts. What do you predict would be the phenotype in terms of segment identities? a) T1 T1 T1 T1 T2 T2 T2 T2 b) T1 T1 T2 T2 T2 T2 T2 T2 c) T1 T2 T2 T2 T2 T2 T2 T2

10. The phenotype of an embryo exposed to excess retinoic acid is like a: • Loss of function Hox mutation • Gain of function Hox mutation

11. Loss of function mutations in a Hox gene generally result in homoeotic defects (normal structures formed in abnormal places) that can be described as: a. posterior-to-anterior transformations b. anterior-to-posterior transformations

12. Hox genes encode: a. Paracrine ligands b. Juxtacrine ligands c. Endocrine ligands d. Transcription factors e. Receptors

13. The phenotype of the Hoxc8 knockout in mouse (shown in figure 14.3 Wolpert) can be described as a a. posterior to anterior transformation b. anterior to posterior transformation