Лекция 3 (А. П. Перевозчиков). Развитие и эволюция глаз. Как эволюционировали глаза ?.
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1. (Camera Eye) () .
Found in the clam Pecten and a few ostracod crustaceans. This produces bright but reasonably hazy picture.
Pit or Cup eyes are found mainly in mollusks and can only resolve location of objects.
h2=0.5 (common heritability), i and V both = .01 (low values for conservative estimation), therefore
R=.00005m, so small variation and weak selection produce a .005% change per generation. So
1.00005n=80129540 so n=363992 generations.
Next, the eyespot dimples inward. This increases visual acuity by allowing the eye to sense the direction the light is coming from better than a flat eyespot. Planarians (flatworms) have such dimpled eyes
Around this point the pit begins to fill with a clear jelly-like material. It is thought that producing this jellywould be rather simple for most creatures - probably no more than one or two mutations. It is suggested that this jelly or slime helps to hold the shape of the pit, and helps to protect the light sensitive cells from chemical damage. And, the jelly might also keep mud and other debris out of the eye
Next, a lens is needed. To get a lens, a ball-shaped mass of clear cells with a slight increase in the refractive index is needed. Once this mass is formed, it can be refined with very slight increases in the refractive index to produce greater and greater visual acuity An examples of such an eye with a "primitive" lens is found in the Roman garden snail (Helix aspersa)or slug
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, . PAX6: eyeless, twin of eyeless, eyegone = mouse/human Pax6.EYA: eyes absent = mouse/human Eya1, Eya2, Eya3, Eya4.SIX:sine oculis/D-Six4 = mouse/human Six1, Six2 / Six4, Six5.Optix = mouse/human Six3, Six6.DACH:dachshund = mouse/human Dach1, Dach2.
. . (Photograph courtesy of T. Venkatesh.)
Differentiation of photoreceptors inthe Drosophila compoundeye. The morphogenetic furrow (arrow) crosses the disc from posterior (left) to anterior (right). (A) Confocal micrograph of a triple-labeled late larval eye/antennal imaginal disc,showing hairy expression in green ahead of the morphogenetic furrow (arrow). Within the furrow, the Ci protein (red) is expressed as a consequence of the Hedgehog signal. (It will activate the decapentaplegic gene.) The neural specific protein, 22C10, is stained blue in the differentiating photoreceptors behind the morphogenetic furrow. (The bluehorizontal line of staining is Bolwegs nerve.) (B) Behind the furrow, the photoreceptor cells differentiate in a defined sequence. The first photoreceptor cell to differentiate (shown in blue) is R8. R8 appears to induce the differentiation of R2 and R5, and a cascade of induction continues until the R7 photoreceptor is differentiated. (A, photograph courtesy of N. Brown, S. Paddock, and S. Carroll; B after Tomlinson 1988.)
Wolff, T. and Ready, D. F. (1993). . In: The Development of Drosophila melanogaster. Cold Spring Harbor Laboratory Press. Vol. 2 Pp. 1277-1325
Summary of the major genes known to be involved in the induction of Drosophila photoreceptors. For development to continue beyond the differentiation of the R8, R2, and R5 photoreceptors, the rough gene (ro) must be present in both the R2 and R5 cells. For the differentiation of the R7 photoreceptor, the sevenless gene (sev) has to be active in the R7 precursor cell, while the bride of sevenless gene (boss) must be active in the R8 photoreceptor. From Gilbert, 2003; After Rubin 1989.)
Ciliary photoreceptors require transducin, a member of the Gi/o-family of G-proteins, whereas rhabdomeric photoreceptors use a member of the Gq/11-family of G-proteins
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