Wednesday, April 15, 2009
Melanin Paint
On pages 208-210, Caroll discusses his own research into the wing patterns of the fruit fly Drosophilia melanogaster. He uses the metaphor of paintbrushes and black paint to describe genes that encode for melanin-synthesizing enzymes. Explain in biological terms what exactly Caroll means by this, including a description of what the "switches" are and how this expands to a "tool kit" that allows for the many different wing patterns. Caroll also explains that the "paintbrush gene has other separate switches that control how it is used in other body parts." Explain why such complexity has arisen around the evolution of a single black spot.
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There is a great variation in wing patters, as seen by FIG 8.7. As Carroll states, by changing and playing around “with the switches of pigmentation genes, flies have evolved a great diversity of wing patterns under both sexual and natural selection” (210). The most common pattern is a black spot near the tip of the wing. Even though this seems like a simple design, it actually could be a process of “multistep series of changes” (208) in order for the spot to evolve. In fact, most physical traits do not just appear but evolve over and build up over many generations, just like the wings of fruit flies.
ReplyDeleteOne reasons that fruit flies develop these patters is in order to find a mate and for sexual reasons. The males are usually the only ones restricted to the pigment patters and “are displayed during elaborate courtship dances…in front of the female”( 208). But when the females stop selecting on the traits then there is less pressure to maintain it so it disappears and the wing patterns change. Another reason that the wing pattern might change is that there is a mutation in the switch that made the spot and it becomes inactivated and stops producing that pattern.
So it seems as if the wing patterns evolve over time when “old” genes learn new tricks. What this means is that there are different variations that could happen but the ones that are more common and would attract more females, in this case the black spot at the tip of the wing, is the one that evolves.
Due to the studies of Carroll and his colleagues at the University of Wisconsin-Madison , there have been a lot of questions answered regarding fruit fly wing patterns. The researcher said their findings emphasize the evolutionary significance of "pleiotropic" genes -- those with multiple on-switches that enable the expression of a single gene in different tissues or at different stages of development. This explains why the wing patterns change and evolve over time. Their genetic studies focused on the role of DNA segments called cis-regulatory elements that were thought to be involved in the evolution of wing spots. The researchers' comparison of the different species revealed that all the gains or losses of spots involved mutations that altered CREs for the yellow gene. It showed how the fruit flies use a gene that is already active in the wing and modifies the patter. The scientist thinks that this is strong clue to how nature invents, which is by using material that is already available
http://www.biology-online.org/articles/fruitfly_study_shows_evolution.html
http://www.hhmi.org/news/pdf/carroll3.pdf
Melanin Paint
ReplyDeleteOn pages 208-210, Caroll discusses his own research into the wing patterns of the fruit fly Drosophilia melanogaster. He uses the metaphor of paintbrushes and black paint to describe genes that encode for melanin-synthesizing enzymes. Explain in biological terms what exactly Caroll means by this, including a description of what the "switches" are and how this expands to a "tool kit" that allows for the many different wing patterns. Caroll also explains that the "paintbrush gene has other separate switches that control how it is used in other body parts." Explain why such complexity has arisen around the evolution of a single black spot.
A certain creature, the Drosophilia melanogastor has a great variety of black pigment patterns on its wing which becomes a selective advantage, allowing it to survive and reproduce. Some have said that the wing spots and pigment patterns are crucial to the courtship ritual of the fruit fly. The exact theory and reason behind the spot is still quite unknown, but for now, all that we are concerned about is that it is involved in the sexual rituals of the fruit fly and thus affects the evolutionary outcome in the future. It affects the evolutionary outcome because when females use the spots to select a mate, it becomes a selection force such as predation and such and decides which traits get passed on to the following generation and which traits die off as inadequate. This slow selection of gene variation eventually narrows down the gene pool and highlights a certain genetic trait and code to continue to be passed down into further generations.
The method behind the creation of the patterns of the pigment pattern is quite interesting. The creation of the spots involves enzymes that synthesize melanin. “The patterns are controlled by switches that surround the coding part of each paintbrush gene.” (208). To be more specific, the CIS-regulatory elements (CRE) are DNA segments that nestle around DNA sequences that code for specific proteins and dictate where and when a gene is turned on or off in the body, similar to TATA box in the DNA sequence in the promoter area. This is where RNA polymerase would attach on to transcribe the DNA sequence in order to obtain mRNA to translate and synthesize protein and enzymes to create those certain black spots on the wings. Whenever the CRE would vary then the transcription and translation of the DNA sequence would vary thus resulting in a variation in proteins which leads to a variation in physical traits. The CRE is crucial to understanding the evolutionary pathway because it shows that CRE can be mutated without compromising the basic function of the gene resulting in variation without permanent mutation. This further shows that the wing pattern’s were not a created from genetic sequence scratch but rather just read differently from a wide array of DNA code already available for a creature. This shows how organization narrows down for complex processes and specific needs, allowing a specific trait to energy from the convoluted gene pool. IT shows how “evolution is a tinkerer.”
This gene is also seen to be a pleiotropic gene. A gene that influences multiple phenotypic traits. Consequently, a new mutation in the gene will have an effect on all traits simultaneously. This can become a problem when selection on one trait favors one specific mutant, while the selection on the other trait favors another mutant. So not only does this trait affect the wing pattern but it also affects other body parts which gives evolution an artistic freedom to play with the regulatory elements without making drastic and permanent change to the genetic code in a body.
Switches that affect the fruit flies black spots could be the same switches like the pitxl homeobox gene in the stickleback fish. The pitxl gene is part of the protein that binds to DNA when the protein functions as a transcription factor as described in above. This protein allows it to attach to the DNA code and help it read it. This gene thus affects the transcription of the gene which controls gene expression and soon development within the body. Other switches are mentioned above such as repressors or corepressors, inducers, or anything that involves in the whole transcription translation process.
With so many factors affecting the black spot of the fruit fly many complexities arise from it. The selection process is especially intense as described by Juliya and I. Without this complexitiy the fruit fly would not be able to find a mate, reproduce, and survive. It would become insignificant in the world.
http://www.biology-online.org/articles/fruitfly_study_shows_evolution.html
http://en.wikipedia.org/wiki/Pleiotropy
http://news.bio-medicine.org/biology-news-3/Fruitfly-study-shows-how-evolution-wings-it-7135-1/
http://www.innovations-report.com/html/reports/life_sciences/report-58239.html
The pigment patterns on the wings of the cousins of Drosophila melangastor are very important for their survival. Males attract females with dances of courtship by means of flashing the patterns. The enzymes responsible for "painting" the patterns on a fruit fly's wing is "controlled by switches that surround the coding part of each paintbrush gene". This, in biological terms, exemplifies gene regulation and expression. These genes are turned off and on before transcription, thus regulating whether or not the enzyme is created during the translation of RNA. The presence of multiple “switches” gives rise to the complexity of the patterns that are displayed on the wing. The complexity of the patterns probably developed due to competition for mates. It is more advantageous for wings to have a more elaborate pattern in order to have a higher chance of winning a mate. The flies with more complex pigment patterns had a selective advantage because it enhanced their sexual success.
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