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5.3 Eye & Lens Induction — Test 1
Q1. During vertebrate eye development, the lens is induced in the head ectoderm by the:✓ Optic vesicle
Q2. In vertebrate lens induction, the optic vesicle acts as the:✓ Inducer of competent head ectoderm
Q3. The transcription factor Pax6 is essential for eye development because it:✓ Makes the head ectoderm competent to respond to the optic vesicle
Q4. In Xenopus, lens induction can occur even without the optic vesicle if the head ectoderm has first been primed by the:✓ Anterior neural plate
Q5. Studies in amphibians suggest the FIRST inducers of the lens may be the:✓ Foregut endoderm and heart-forming mesoderm
Q6. Lens induction, in which the neural plate primes the ectoderm (via Pax6) so it can respond to the optic vesicle, is best described by:✓ Induction and competence
Q7. Wolffian lens regeneration in amphibians occurs when the lens is lost and is regenerated from the:✓ Iris (pigmented epithelial) cells
Q8. Wolffian lens regeneration involves iris cells undergoing:✓ Dedifferentiation and then trans-differentiation into lens cells
Q9. Pax6 is sometimes called a 'master control gene' for the eye because:✓ Its ectopic expression can induce ectopic eyes (e.g. in Drosophila)
Q10. The thickening of head ectoderm that forms in response to the optic vesicle, before the lens, is the:✓ Lens placode
Q11. Reciprocal induction in the eye means that:✓ The optic vesicle induces the lens, and the lens in turn influences the optic cup/cornea
Q12. If head ectoderm lacking Pax6 is placed under an optic vesicle, it will:✓ Fail to form a lens (it is not competent)
Q13. The lens placode invaginates and pinches off to form a hollow ball called the:✓ Lens vesicle
Q14. The optic vesicle, which induces the lens, grows out from the:✓ Forebrain (diencephalon)
Q15. After the lens vesicle forms, its inner cells elongate and synthesise large amounts of:✓ Crystallin proteins
Q16. The optic vesicle folds inward to form a double-walled structure called the:✓ Optic cup
5.3 Eye & Lens Induction — Test 2
Q17. The cornea develops from the ectoderm that overlies the lens after induction by the:✓ Lens (reciprocal induction)
Q18. Pax6 is conserved enough that the mouse Pax6 gene can induce ectopic eyes in Drosophila, showing that:✓ The genetic program for eye formation is deeply conserved across animals
Q19. Aniridia in humans, a defect of the iris, results from mutations in:✓ PAX6
Q20. The fact that lens induction needs both the optic vesicle AND prior priming of the ectoderm shows that induction can be:✓ A multi-step process with several sequential signals
Q21. In Wolffian regeneration, the new lens forms specifically from the ____ margin of the iris:✓ Dorsal
Q22. Wolffian lens regeneration is remarkable because the new lens forms from a tissue (iris) that is NOT its normal embryonic source. This is an example of:✓ Trans-differentiation (one cell type becoming another)
Q23. If the optic vesicle is surgically removed before it contacts the ectoderm, the usual result is that:✓ No lens (or a much-reduced lens) forms
Q24. Placing the optic vesicle under non-head (e.g. trunk or belly) ectoderm usually fails to induce a lens because that ectoderm:✓ Is not competent (lacks the priming/Pax6)
Q25. The reciprocal nature of eye induction ensures that the lens and retina:✓ Are correctly aligned and sized to work together
Q26. Lens fibre cells become transparent in part because, as they mature, they:✓ Lose their nuclei and most organelles
Q27. Sequential induction in the eye (endoderm/mesoderm → neural plate → optic vesicle) is a good example of how complex organs are built by:✓ A cascade of tissue interactions over time
Q28. The optic cup's outer layer becomes the pigmented retinal epithelium, while the inner layer becomes the:✓ Neural retina (photoreceptors and neurons)
Q29. Eye development illustrates 'competence' particularly well because only certain ectoderm responds to the optic vesicle. Competence is best defined as:✓ The ability of a tissue to respond to a given inducing signal
Q30. The classic experiments showing that the optic vesicle induces the lens were important because they demonstrated:✓ Embryonic induction — one tissue directing the fate of another
Q31. Compared with the original embryonic lens, a Wolffian-regenerated lens is notable because it forms:✓ Without going through the normal lens-placode stage
Q32. Overall, eye/lens development is a model system because it cleanly shows:✓ Induction, competence, reciprocal signalling and (in newts) regeneration