Tooth Pick Fish

We are currently learning about genetics in my science class. We’ve learned how to determine what alleles (physical traits) an offspring would inherit from its mother and father. Just recently we performed an experiment that was related to both genetics and ecology. We were given 24 toothpicks (8 green, 8 red, and 8 yellow) that represented three different form of a gene that controls one fish trait: skin color. The first step in our experiment was to make a first generation of fish. This was done by randomly pulling out genes (toothpicks) in pairs. This simulated the way offspring are formed by sperm from the male fish combining randomly with eggs from the female fish. In this experiment, the color green was the dominant gene, which meant that if a fish had a green gene, then it would have green skin. Since green was a dominant gene it was represented by “G”. The colors red and yellow were recessive genes, which meant that a fish would need two red genes (toothpicks) to be red. This also meant that a fish would only be yellow if it had two yellow genes (toothpicks). Since, they are recessive genes they are represented by “r” (for red) and “y” (for yellow). A red gene was co-dominant to a yellow gene. This meant that the combining of a red gene and a yellow gene would produce a fish with orange skin. This is called incomplete dominance, which means the two traits are mixed.

A way that we can examine an organism’s alleles is by analyzing their genotypes and phenotypes. The phenotypes are what the offspring actually look like. In this case, the phenotype is the skin color of the offspring fish. The genotypes are the genetic traits in an organism. It has to do with the genetic coding of an organism. In this chart, the genotypes are represented by letters to show the offspring’s alleles. In this experiment, the phenotypes and genotypes were as follows:

Green: GG, Gr, Gy
Red: rr
Yellow: yy
Orange: ry

As you can see, the phenotype is the color of the fish and the genotype represents their genetic coding. From this chart we learn that an offspring with green skin had a parent who had green skin. Since green is the dominant gene the offspring automatically inherited the green skin color no matter the skin color of the other parent. An offspring with red skin came from parents who both had red skin. An offspring with yellow skin came from parents who both had yellow skin. An offspring with orange skin came from one parent who had red skin and the other parent who had yellow skin. From the information from this chart, we can say that two red fish cannot have offspring with green skin because neither parent had a green gene. We can also say that two orange fish can have a red offspring because both parents have a red gene. From this chart, we can also determine that two green fish cannot produce an orange offspring. Since green is the dominant gene the offspring automatically inherits the green skin color no matter the skin color of the other parent.

Total number of each color of offspring:
First Generation: Lots of seaweed and algae everywhere
6 Green Fish, 1 Red Fish, 1 Yellow Fish, 4 Orange Fish

Second Generation: Lots of seaweed and algae everywhere
8 Green Fish, 1 Red Fish, 0 Yellow Fish, 2 Orange Fish

Third Generation: Lots of seaweed and algae everywhere
8 Green Fish, 0 Red Fish, 0 Yellow Fish, 3 Orange Fish

Fourth Generation: Lots of seaweed and algae everywhere
6 Green Fish, 2 Red Fish, 1 Yellow Fish, 2 Orange Fish

Survivors: Seaweed and algae die
0 Green Fish, 2 Red Fish, 1 Yellow Fish, 2 Orange Fish


My first generation of fish consisted of 6 green fish, 1 red fish, 1 yellow fish, and 4 orange fish. In the experiment, our fish lived in a stream that was very green and had lots of vegetation and algae covering the streambed and banks. Because of the environment they lived in, the yellow fish did not survive or reproduce because their color stuck out in their green environment and it was easy for them to be seen by predators. My second generation of fish yielded 8 green fish, 1 red fish and 2 orange fish. I notice that the number of green fish has increased. The green fish are well-camouflaged so the live longer and can reproduce. My third generation of fishes yielded 8 green fish and 3 orange fish. I notice that my second and third generations do not have any yellow fish. Since the yellow fish cannot camouflage themselves, they have fallen prey to predators. This has prevented them from reproducing and has caused their population to decrease. But fortunately, the yellow allele has not disappeared. It is still carried by the orange fish. The same situation can also occur in the wild. Animals that have traits suited for their environment can hide from predators, live longer and can reproduce, thus increasing their population. Animals with traits that do not suit their environment will fall prey to predators. Their population ends up decreasing and the traits they carry will disappear. For the fourth generation, I came up with 6 green fish, 2 red fish, 1 yellow fish, and 2 orange fish. During the fourth generation, an environmental disaster occurred. Factory waste was dumped into the stream and killed most of the seaweed and algae. This meant that there were only rocks and sand left, which made good camouflage for the red, yellow, and orange fishes. Since there was no greenery left, all the green fish were easily spotted and eaten by predators. The population of the green fish disappears. The survivors of the environmental disaster consisted of 2 red fish, 1 yellow fish, and 2 orange fish. The population of fish had decreased because its environment changed and they fell prey to predators.

In the beginning of the experiment, I noticed that the fish with yellow alleles were disappearing because of predators. The population of the yellow fishes dwindled while the green fish population flourished because the green fish possessed a dominate gene color and had the ability to blend in with its environment. This allowed them to survive and reproduce. By the third generation, there were less yellow fish in the third generation than the first generation. This can also happen in the wild because animals that have traits that cause them to be easy prey start to disappear. By the end of the experiment, an environmental disaster occurred and eliminated the green fish’s camouflage. This made the green fish easy prey for predators. The population of the green fish disappeared after the environmental disaster. Since green was a dominant allele, every fish that had a green allele would automatically be green. The green allele disappeared when the green fish perished in the environmental disaster. Future generations of fish will never inherit the green allele. The red, yellow and orange fish posses the red alleles and the yellow alleles. Since they survived the environmental disaster, the red and yellow alleles survived. This means that the red and yellow alleles can be passed on to future generations of offspring. This experiment showed me that dominate genes can be quickly eliminated while recessive traits can survive because they are hidden.

After the experiment was completed, I wondered what would happen if the lab had been changed. If both the yellow and red fish did not survive or reproduce because their colors allowed them to be easy seem by predators, what would happen? From the experiment, I concluded that the decrease in the red and yellow fish population would cause a decrease in the orange fish population as well. Fish with orange skin come from a red fish parent and a yellow fish parent. If the population of red fish and yellow fish decrease then the population of the orange fish will decrease.

By: greendragon