The wings of butterflies and moths consist of a colorless translucent membrane covered by a layer of scales the name of the order is Lepidoptera, meaning "scaly wings".
The scales overlap like roof tiles and completely cover the membrane, appearing as dust to the naked eye. The iridescence is caused by multiple slit interference. Sunlight contains a full range of light wavelengths. Light is a wave. If the crests and the troughs of the waves are aligned, or in phase, they will cause constructive interference, and iridescence is the result.
One light wave hits the first groove, and a second light wave travels half of a wavelength to another groove, and is then reflected back in phase with the first. If the crest of one wave meets the trough of another wave out of phase , they will cancel each other out, as destructive interference occurs. Blue light has a wavelength range from to nm. The slits in the scales of the Morpho are nm apart. Because the distance between slits corresponds to half of the wavelength of blue light, this is the wavelength that undergoes constructive interference.
The slits are attached to a base of melanin, a material that absorbs light, further strengthening the blue image. Detailed views of scales from the wing tops, and wing undersides. Notice the veins in the magnified views.
This stems from normal organic pigments, rather than physical structure, and does not change with viewing angle. The first are pigmented colors which are simply ordinary chemical pigments that absorb certain wavelengths of light and reflect others.
An example would be that the shades of brown and yellow seen in most butterflies comes from melanin, the same pigment that tans your skin when you sit in the sun.
When light hits the object it absorbs all the colors except the shades that create brown or yellow. Butterfly wings are covered by lots of little scales which layer on top of each other and are separated by little pockets of air. Because of this structure color appears to shimmer and shift as an observer moves is actually a light effect known as iridescence. Iridescence occurs when light comes through transparent multilayered surfaces and is reflected more than once.
Butterflies have four different life stages during development. These are the embryonic stage which takes place inside the egg , the larval or caterpillar stage, the pupal stage, and the adult stage.
Eggs are laid on the leaves of specific plants and the caterpillars that hatch from the eggs eat these leaves until they enter the pupal stage. The pupal stage is when most of the larval body tissues are dissolved and re-formed to create the adult butterfly that finally emerges. The wings of butterflies are formed from a group of cells that are set aside during the embryonic stage, in the form of imaginal discs. These imaginal discs grow inside the larval body as the larvae grow, but in the pupal stage the imaginal discs move to the outside of the body and develop their final size and shape.
You can easily see the front wings of a future butterfly by carefully examining the two sides of a pupa. Adult wing patterns gradually develop on the wing imaginal discs as these discs grow into the adult wings. This division happens because certain genes sections of DNA that contain specific instructions to build the organism become expressed only in one surface of the wing, say the dorsal surface, but not in the other.
After this stage, prepatterns are laid out on the disc, due to the expression of different genes in different positions of the wing Figure 1B. At this early stage, it is already clear that the prepatterns are different on the dorsal and ventral wing surfaces. In a later stage, colors appear in the prepatterns because pigmentation color genes become activated [ 1 ].
Using the analogy of a piece of paper again, we can create compartments in the paper by drawing lines and creating folds as shown in Figure 1C. Then, we can draw a picture on one side of the paper that represents a prepattern, and finally we color the picture using different color combinations to get the final adult pattern Figure 1C. Scientists have studied wing development in fruit flies scientific name: Drosophila melanogaster for many years and have identified a lot of genes important for creating compartments and patterns.
Because wing development in fruit flies and butterflies is very similar, the initial stages of wing development, such as creation of compartments in butterfly wings, has come to be understood quite well through the study of fruit flies. However, butterflies are different from flies in that butterflies have intricate and colorful wing patterns. Researchers have been quite successful at identifying numerous genes that create these patterns. For example, many genes involved in the development of patterns that look like eyes, called eyespot patterns, have been identified.
In the butterfly species Bicyclus anynana , genes called spalt and distal-less are expressed in the centers of eyespots, and, spalt is also expressed in the black ring. So, based on these studies and the similarity in development between fly and butterfly wings, we hypothesized that a gene called apterous A might be responsible for creating different dorsal and ventral wing patterns in butterflies.
We selected this gene because, in the wings of flies and butterflies, it is expressed only on the dorsal surface and is absent from the ventral surface [ 3 , 4 ]. We used the butterfly B. To show that this gene is responsible for creating different surface-specific patterns in butterflies, we needed to delete it and look at wing patterns in butterflies that did not have this gene.
If apterous A is indeed responsible for creating a dorsal pattern that is different from the ventral pattern, then when it is deleted, the dorsal pattern should become similar to the ventral pattern.
The CRISPR-Cas9 technique is a powerful new technology that has made it possible for scientists to easily mutate genes and delete gene functions [ 5 ]. This system was initially identified in bacteria as an immune response to protect bacteria from harmful agents such as viruses [ 5 ]. When scientists use the CRISPR-Cas9 technique to delete certain genes in animals, they can then study the animals to see what happens when that gene is missing.
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