Monday, March 30, 2009
Complexity in Fruit Fly Wing Patterns
On page 208, Carroll notes that the “fruit fly Drosophila melanogastor has pale wings but its many cousins in the large family to which it belongs display a great variety of black pigment patterns”. Explain the pigment pattern and the purpose it serves. Additionally, explain how the diversity in fruit fly wing patterns are created using Figure 8.8 on page 211.
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dibs, auvinen please dont answer it 5 minutes before i do again
ReplyDeletethank u very much,
Scotty Lu
ill do it by tonight
The diverse and wonderful world of insects is definitely a huge group of species to observe and study. 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.
ReplyDeleteThe 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 emergy 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.
"And studies of phenomena such as fruit fly wing spots show how evolution is not some one-off process. It repeats itself over and over.
They show that there is more than one way to tinker with the same gene, and by extension, to independently evolve the same trait," Carroll said.
http://www.biology-online.org/articles/fruitfly_study_shows_evolution.html
http://en.wikipedia.org/wiki/Pleiotropy
On page 209, Carroll discusses the patterns of the wings of fruit flies, specifically Drosophila melanogaster. The visible black spots on their wings come from enzymes synthesizing melanin. The enzymes are more abundant when there are more black spots and less abundant when the wings are mostly blank.
ReplyDeleteThe patterns on the fruit flies’ wings really represents the complex evolution of human genes. Rather than simple black spots, the patterns appear because of a complex system of different genes changing or turning on and off. This is how human genes are. There isn’t a simple system where one gene encodes for what is physically shown.
D. melanogaster have been chosen so readily by scientists to do experiments on because of their short generation time and there are an abundance of mutations that arise after every reproduction.
A tool-kit gene is used in this situation where genes can be modified in one area of the body, while not affecting the gene in other areas of the body. Once the spot has been determined, it is often passed down to offspring.
However, many times, this gene is lost. Evolution almost appears to have turned backwards with the disappearance of this trait. This is another good representation of genes in humans. Often, it is a selective advantage, or just a mutation, that causes the loss of a gene. In this case, it was just wing patterns.
Because of the high reproduction rate and the even higher mutation rate among this species of fruit flies, many different patterns of wings have evolved over time. This is attributed to both sexual and natural selection. Often, mating has a lot to do with the pattern on the wings. This causes some patterns to show up in future generations more often than others. It is not only caused by natural selection and mutations.
http://en.wikipedia.org/wiki/Drosophila_melanogaster#History_of_use_in_genetic_analysis
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/Drosophila.html
http://en.wikipedia.org/wiki/Drosophila