Learning from the Fossil Record
Grade 8 Science
Name: Liam and Tyler
Date: 2/23/11
Part1 of Performance Assessment Task
In analyzing the fossils in each layer, the scientists were able to identify some key features that
struck them as interesting. Unfortunately, the digital camera they used to take pictures was
damaged and they are unable to send you pictures at this time. They would like, however, you
to begin determining the possible inheritance of traits seen. They were able to send you the
following descriptions.
Deepest fossil layer: all
short skull and jaw
Long, skinny tail
Long front legs
Long back legs
No flukes on the tail
Next fossil layer:
some
short skull and jaw
Long, skinny tail
Long front legs
Long back legs
No flukes on the tail
Next fossil layer:
all
Long skull and jaw
Short, fat tail
Front flippers
Short back legs
Flukes on the tail
Next fossil layer:
all
Long skull and jaw
Short, fat tail
Front flippers
No back legs
Flukes on tail
some
long skull and jaw
short, fat tail
short front legs
long back legs
no flukes on the tail
By studying present day animals with similar traits, they have inferred that:
1. Long skull and jaw are dominant over short skull and jaw
2. Short thick tail are dominant over long skinny tail
3. Long front legs is dominant over short front legs
4. Long back legs is dominant over short back legs
5. No flukes on tail is dominant over flukes on tail
1
Learning from the Fossil Record
Grade 8 Science
Name: Liam and Tyler
Date: 2/23/11
They ask that you send a report of your findings on the possible genetics and inheritance of
these traits. They do know all of these fossils are related as the area was isolated and no other
animals could come in or go out of the area.
Please include the following in your report.
1. How is it possible for the recessive short skull and jaw trait to change to a dominant
long skull and jaw trait and stay that way permanently?
2. How is it possible for the recessive long, skinny tail trait to change to dominant short,
thick tail trait and stay that way permanently?
3. How is it possible for the dominant long front legs trait change to a recessive short front legs
trait and then turn into flippers?
4. How is it possible for the dominant long back legs trait to change to a recessive short bag legs
trait and then disappear completely?
5. How is it possible for the dominant no flukes on tail trait to change to a recessive flukes on tail
trait and stay that way permanently?
Red text indicates the example that will be used by the teacher to model the process.
Each answer will be scored on the following aspects:
a. Does the reasoning behind the answer make sense and is it possible? 0 1 2 3
b. Is the reasoning behind the answer supported by data (e.g., Punnett Squares, diagrams,
explanations)? 0 1 2 3
c. Where reasoning cannot be found using genetics, is a reasonable prediction made? 0 1 2 3
d. Is the report organized in a logical manner so the reader can understand the explanations
provided? 0 1 2 3
2
Learning from the Fossil Record
Grade 8 Science
Name: Liam and Tyler
Date: 2/23/11
2. In the first fossil layer, all of the organisms had long and skinny tails. This was because all of
the organisms had the ss genotype, homozygous recessive. In the next fossil layer, both the
long and skinny tails AND the short and thick tails came into existence. This means that both
the ss and Ss/SS genotypes were present. The ss genotype was present because the creatures
mated and had children with ss genotypes, which should be the only possible combination.
Outside of genetics, the genes changed and somehow the animals ended up with the short
and fat tail genes. It could have been possible that the short tail had developed through the
environment and the genes changed in response. In the next fossil layer, the animals all had
short, thick tails. This means that only the SS/Ss genotypes existed anymore. This could have
been caused by the long skinny tails causing death to the animals, so all the animals having it
died. Possibly it was dragging through the dirt and making more tracks that could be followed
by predators. In the final layer, all of the animals again had short, thick. While this means
that, yet again, the only genotypes were SS/Ss, it almost completely rules out the possibility of
an Ss genotype existing. If it had been still around in the previous fossil layer, at least some of
the animals in this layer would have been homozygous recessive (ss) and had the long, thin
tails. It would just be too unlikely. This means that all the animals would be SS.
3.
It is possible for the creature to change from long front legs (dominant) to short front legs
(recessive). In the deepest layer, the organisms were either heterozygous or homozygous
dominant. This is because in both situations, the parents relate effectively to their offspring in
the next layer. In the next layer, some had short legs and others had long legs. The presence
of short legs suggests that they had two heterozygous parents because both parents applied
to having long legs and their children could have either had short legs or long. In the case of
the offspring with long front legs, their parents could have either had been homozygous
dominant or heterozygous. In the final two layers, the creature had flippers. A cause outside
of genetics that is probably the reason for the change in its structure was the environmental
adaptations it had to make. Flippers usually appear in a creature when they live underwater
because it helps them swim. There was probably a time where the area where the animal
lived became engulfed with pretty reasonable water levels. In order to survive in their
environment, they probably evolved into a new form. This is the most likely reason why the
dominant long front legs trait changed to a recessive short front legs trait and then turned
into flippers.
4. It is possible for the creature to change from long back legs (dominant) to short back legs
(recessive) and then disappear. In the deepest layer, the organisms were either heterozygous
or homozygous dominant. This is because in both situations, the parents relate effectively to
their offspring in the next layer. In the next layer, some had short legs and others had long
3
Learning from the Fossil Record
Grade 8 Science
Name: Liam and Tyler
Date: 2/23/11
legs. The presence of short legs suggests that they had two heterozygous parents because
both parents applied to having long legs and their children could have either had short legs. In
the case of the offspring with long back legs, their parents were probably heterozygous or
homozygous recessive. Based upon the other traits in the final two layers, you can infer the
species was already beginning to evolve into its environment. This suggests that probably
over time, the back legs had begun to shrink to the point where in the final fossil layer, the
legs had vanished forever. It is also possible that the long legs began to leave because short
legs kept being inherited more often. But I still believe that absence of back legs is due to the
fact of the introduction of flippers to an aquatic environment. Back legs simply became a
burden for the species due to the change of its environment.
5. It is possible for the creature to change from no fluke on tail (dominant) to a fluke on the tail
(recessive). In the first two layers, the organisms were probably homozygous dominant. This
is because in both of the layers, all of the organisms had no flukes. In the last two layers, the
organism gained flukes due to evolution. This is highly likely, once again, due to the change of
the environment. Since the animal gained a fluke on its tail, it suggests that it became an
aquatic creature. Flukes help to allow an animal to swim underwater, being very vital to its
survival in those environments. At the same time it is possible for the organism to have
maintained its heterozygous traits for two fossil layers before permanently converting to
homozygous recessive, but the likeliness is indescribably slim. The organism, once again,
probably changed from having no flukes, to flukes on its tail due to the change of its
environment.
4