Entomology 109
Genetics--Drosophila lab
1. Why is Drosophila melanogaster such an excellent model organism for use in genetic studies?
2. Why is Drosophila melanogaster less than perfect as a model organism for use in, for
example, genetic studies of humans?
3. List the mutants that you see during your visit, and describe what is different about them.
How would you go about obtaining your own Drosophila mutants?
How would you feed and rear them?
4. What is
a. a P element?
b. a recessive trait?
c. a sex-linked trait?
5. Describe how foreign genes are inserted into Drosophila:
What are possible applications of genetic transformations of insects?
Natural selection
Natural selection is the process by which individuals with heritable traits conferring survival
produce more offspring than individuals lacking such traits. This process was described in detail
by Charles Darwin, who was inspired at least in part by certain insect traits that appeared to have
arisen in response to predation pressure. Among these traits are crypsis, homotypism, and
aposematism. In this part of the laboratory exercise you'll examine the nature and value of
protective resemblances in reducing mortality due to predation.
Crypsis/homotypism--Display 1
In this display are several insects that exhibit homotypism.
1. Which orders are represented in this display?
2. What colors predominate among these insects?
3. Why do you think plant surfaces are so commonly represented as models among homotypic
insects?
Hymenopterans and mimics -Display 2
In this display are several Batesian mimicry complexes.
1. To what order do the models belong?
2. To what order do the mimics belong?
3. Why is this complex considered Batesian and not Muellerian?
4. What colors predominate among the insects on display here?
Aposematism and mimicry -Display 3
1. To what order do these models and mimics belong?
2. What colors predominate among insects on display here?
3. What function do these particular colors serve?
Aposematism and mimicry in butterflies-Display 4
1. Based on appearances, what do you think an "intergrade" is?
2. One of these mimicry systems is mislabeled. Can you spot the error?
Aposematism/mimicry experiment
In this experiment, you and your lab partners will serve as predators and jelly beans will serve as
proxies for insect prey. The jelly beans represent a mixture of palatable and unpalatable
(chemically protected) prey. In this experiment, "distasteful" is "hot and spicy”, bitter, or just
plain disgusting. The object of this exercise is for each group of predators to leave remaining in
the bowl as many distasteful prey as possible.
Each group should consist of five "predators." Prey should be sampled at a rate of 1 per minute
until each predator consumes three prey items, with no individual predator consuming successive
prey (in other words, order of prey taking should go 1-2-3-4-5-1-2-3-4-5-1-2-3-4-5). You are
free to communicate among yourselves--inform other predators as to whether or not the prey you
have sampled is palatable or distasteful. After all predators have consumed 3 prey items, count
the remaining number of prey of each color and report your results to the teaching assistant.
He/she will compile the data from the entire class and you will collectively discuss your findings.
NOTE: If you're a Jelly Belly expert, please try to refrain from identifying the flavors associated
with the colors. In general, try to forget your preconceived notions about what colors are
associated with which flavors, just for today.
Record order of prey taken below.
Prey item #
Color
Taste
Prey item #
Color
Taste
1
9
2
10
3
11
4
12
5
13
6
14
7
15
8
Number of prey remaining of each color: