Disease strikes the dragons
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Disease strikes the dragons
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The dragon populations across the island have decided to hold a council of their elders and geneticists in an attempt to learn enough about the problem to protect themselves from further harm. At the council, they compare stories and experiences and learn some important things:
1. Only the dragons from the Swamp, Valley and Mountain populations are affected by this disease. Desert, Ice and Forest dragons have been strangely unaffected.
2. This disease does not seem to be contagious from one dragon to another.
Because of these clues, the council decrees that a genetic study should be undertaken to attempt learn more about this disease.
Genetic study
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The dragons have spent much time studying genetics to date, and have stumbled upon small creatures ideal for these studies. Miniature dragon-like creatures known as drakes, populate much of the island. They reproduce easily and live much shorter lifespans than dragons. These qualities make them ideal for breeding and studying. Because the genetics of drakes are quite similar to those of the dragons, they have been studied extensively.
Mice are another creature that have been studied even more extensively, and the dragons on the island have come a good way toward connecting genetic information between drakes and mice. Doing this, they can take advantage of the fact that much is known about individual mouse genes and apply this to their study of drake genetics.
Breeding and traits
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You learned about genetic recombination, or crossing over, earlier. This is the key to studying drake genetics to search for a disease gene.
Remember our dragons with plates earlier? The dragons didn't yet know where the gene responsible for plates is located. You did find out that by breeding two separate strains of dragons together, those that had plates and those that didn't, you got a mix of the two kinds. Try this again below and verify it for yourself.
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To find out more about where a gene is located, we can take advantage of the genetic recombination—or "crossing over"—that you used to help Molthwan and Lucenne have a baby with certain traits.
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You may have noticed that these dragons are similar to Molthwan and Lucenne. If no genetic recombination occurred, they would not be able to have a child with wings and no legs.
Use this fact and the pedigree space below to breed some children from this couple. Notice that you can change the number of offspring by changing the number in the input box and by using the dropdown menu to indicate a fixed number or a range of offspring.
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Just like Molthwan and Lucenne, these dragons shouldn't have had any children with wings and no legs. Because you found some, genetic recombination must be taking place. Breed some children again, and use the chromosome tool to examine some of the dragons. Can you find evidence in their genes to prove your case? Describe one piece of evidence you find in the box below, and take a snapshot for your lab notebook to show this evidence.
Mega-breeding
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Now take another look at the dragons you bred. Do they all have plates? If genetic recombination is taking place, the gene that causes plates must be "scrambled" in this population of children, just like the genes for wings and legs. Find two children of these dragons and breed them together. Breed the same children together multiple times to make a lot of generation F3 children.
Using the offspring
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Let's think about what these chromosomes must look like. If the genes have crossed over at random locations, the set of children you bred will represent a varied patchwork of genes. If we have enough of these, we can compare the genes through a process known as QTL analysis and see where it is most likely that the gene for a trait is located.
Select the children you created with the pointer and save them. Then move to the next section to look at a QTL analysis of this population of children.
QTL Analysis
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This is a plot of what is called a QTL analysis. It was created by breeding two strains of dragons together, one that had a certain trait, and another that didn't, then breeding their children to make many offspring, as you did in the previous section. Some of the many F3-generation children you made had plates, and others didn't.
Because the children's genes were crossed over at many different points, we can use statistics to determine where the gene for plates is most likely to occur. This graph shows how likely it is that the gene for plates occurs at certain places on a chromosome.
Pinpointing a Peak
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Your goal is to find out what is causing this debilitating disease among certain dragons. Remember that you have only Drakes on which to do experiments, and that the various strains of Drakes are matched to various groups of dragons.
Recall that the Mountain, Valley and Swamp dragons are the only strains that are affected with this disease.
Experiments cost money and take time, so you will only be able to perform experiments on a few crosses. Use what you already know about Drakes to help you select which strains to breed in experiments and how many Drakes to use in each experiment. Make sure to keep watch on your budget so you don't run out!
When you find intervals you think you should explore, take notes on what the intervals are. You can explore them with a link on the next page.
QTL Analysis
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