Amanda Barry, Colette Gilbert, Jack Hobbie
Part 2 of Performance Assessment Task
Part 1 of Performance Assessment Task – Skull Model
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?
 Since long skull and jaw are dominant over short skull and jaw, since all the organisms in
the deepest fossil layer have short skulls and jaws, they must be homozygous recessive
(tt) , for short skull and jaw. In the first fossil layer, something in this animal’s
environment could have changed, because the animal’s genes cannot change on demand.
The genes went from recessive to a dominant genotype. The short skull and jaw had to be
affected by the environment. In the deepest fossil layer, there are medium sized trees,
small shrubs and many small creeks. Sunlight wouldn’t be getting through the ozone
layer and would not be hitting the organisms often, because of the medium sized trees. If
there is sunlight, but the trees block the sunlight from hitting the animal, the genes
would stay the same. This is how the animal had its gene to begin with. There are no
mutations to this animal to cause it to change. There is no excessive sunlight because the
trees shade the animals, there is no pollution, no radiation, no chemicals, no cigarette
smoke and no drugs in this animals system because it is so far back in time, that these
side effects haven’t been “born” yet. Nothing can happen to cause a mutation good or bad
yet.
 In the next fossil layer, there were some organisms with short skulls and jaws and some
with long skulls and jaws. The ones with short skulls and jaws were offspring of the
organisms in the deepest fossil layer. ( tt x tt = all tt offspring ) The organisms with long
skulls and jaws cannot be explained genetically because they require at least one
dominant trait (Tt or TT). Since this is not possible, coming from homozygous recessive
parents the reason for this trait must be due to a change in the genes. In this fossil layer,
the trees disappear; taller grasses, small shrubs and swampy areas become the
environment. In this case, the sunlight can reach the animals because the sunlight would
pass through the water where the animal might live. Something made the trees become
extinct, and because there would be excessive sunlight hit the animal to cause a mutation
in the animal that would become an advantage and be permanent. Some of the animals
are starting to get a new mutated gene. Half of them have changed. Some of the
organisms have the dominant long jaw and skull while others have the recessive short
skull and jaw. We don’t know if the animal’s mutation is an advantage to its environment
yet or not, because half of these organisms have the mutated gene. For it to be a positive
effect, the animal will have offspring with that gene to help it survive longer. If it is a
negative effect, the animal will die with the mutated gene and the n the gene for recessive
short skull and jaw will continue in these types of animals.
 In the next fossil layer, all the organisms had the dominant long skull and jaw trait. This
most likely came about by the cross between the TT and tt organisms resulting in all the
offspring coming out to be Tt. It could have been a cross between Tt and tt but some of
the offspring probably would have come out tt (short skull and jaw). Therefore the TT
and tt cross is more likely. The offspring in the next fossil layer all have the mutated gene
for the long dominant jaw. It started as recessive short jaw. Mutation is an advantage
because otherwise, the animal would die off, not growing in numbers. Because the
excessive sunlight this animals gets in its environment with tall grasses, small ponds and
swampy areas, the long jaw and skull must be effective and help it survive longer than if
it would’ve with the short skull and jaw. Since the animal now has more water in this
environment, it has to have a long jaw because of the food it eats is now under water. For
the animal to survive, it must have an advantage, which is the long jaw that stays
permanent for it to be a mutation that is an advantage.
 In the final fossil layer, all the organisms had the dominant long skull and jaw trait
again. This had to come about due to the Tt x Tt cross resulting ion 75 % having the
Amanda Barry, Colette Gilbert, Jack Hobbie
Part 1 of Performance Assessment Task
dominant trait (long skull and jaw) and 25% recessive trait (short skull and jaw). For
some reason the short skull and jaw organisms could not survive beyond birth (probably
due to something in the environment where they needed long jaws and skulls) leaving
only the dominant organism (TT or Tt) to live to adulthood and continue breeding.
Eventually all organisms would end up with TT only, since the chance of having t became
inferior because they could not survive beyond birth. In this fossil layer, traces of the
environment that were found near the organisms’ fossils were larger deep lakes and
many aquatic plants. This means that the animal’s mutation also had to be an advantage
for the animal to continue living. Since the long skull and jaw is still the genotype and it
must help where it lives. Since the environment is now mostly water, it has to be able to
survive in water with a long skull and jaw. It must help the animal when it gets food or
takes care of it’s young. Otherwise, the animal would be extinct because the mutation
wouldn’t help it survive in the changing environment and would die off. The animal
must have the mutation from excessive sunlight, because the trees in the beginning must
have only shaded it partially, and when something happened to those trees, the animal
got much more sun on it to cause the mutation when the environment started becoming
mostly water.
a. Does the reasoning behind the answer make sense and is it possible?
b. Is the reasoning behind the answer supported by data?
c. Where reasoning cannot be found using genetics, is a reasonable prediction made?
d. Is the report organized in a logical manner so the reader can understand the
explanation?
How is it possible for the recessive long, skinny tail trait to change to dominant short, thick tail
trait and stay that way permanently?
In the first layer, the animal started out having a long skinny tail, which was recessive, (tt). In
the next layer closest to the surface, the animal now has some of the existing animals have a long
skinny tail, while others have fat, short tails, which were dominant, (Tt). If the long skinny tail
didn’t have the genotypes of Tt, then there wouldn’t be a possibility of having a new type of tail,
short, fat tails with the genotypes of Tt would be the only way that the tail could change to long
skinny tails or no tails. Since the long skinny tail was the one that started out already there
would be only one way for the long skinny tail to turn into the short fat one is to mutate. That is
the only possible way. In the continuing layers closer to the top of the surface, the animal stays
having a short, fat tail. It gets a short fat tail permanently that means it must have gotten to the
genotype of TT by going through reproduction. There is a 100% chance of the animal getting a
long skinny tail, (recessive – tt) and a 0% chance of the animal getting a short fat tail,
(dominant-Tt), but since they animal went through a mutation on little t turned in the big T so
now it’s a 50/50 chance of a small or long tail, later on when it was dominant the tail’s other
little t mutated into the big T so now its 100% chance of having a short tail. Every time there is
an offspring born, there is now 100% chance the animal to have a short tail. This animal started
out having a recessive short tail, and went to having half of the animal’s offspring with the
genotypes for short recessive tails, and half dominant long tails. Then the animal continued
having the dominant short tail, to permanently have the mutation in the animal’s gene that
controls the tail in the DNA. When the animal had the long dominant skinny tail, and then
mutated to half the offspring having the dominant fat short tail, that had to be caused by a
permanent change in the DNA. The animal must have been in a changing environment, which
caused the cells to change in the offspring, but when the animal was full grown, you wouldn’t see
the changed because the animal already “read” the DNA that controlled the tail. Because the
mediu sized trees shaded the animal from some of the sun, nothing would have happened to th
animal because nothing would have caused the animal to mutate because there was no
Amanda Barry, Colette Gilbert, Jack Hobbie
Part 2 of Performance Assessment Task
pollution, radiation, drugs, cigarette smoke, excessive sunlight or chemicals yet. In the next
fossil layer, the trees disappear and they are replaced with taller grasses, smaller shrubs, and
swampy areas. Which means more sunlight will be hitting the animals and if there is an
excessive amount of it, it could cause a mutation through natural factors. If it is a positive, it
stays permanent and keeps the animals alive, and since that mutation stays that way through all
the layers, it must be an advantage in the now watery environment. After this fossil layer, it
becomes taller grasses, small ponds, and still swampy, and even closer to the surface the
environment is large, deep lake with many aquatic plants.
How is it possible for the dominant long front legs trait change to a recessive short front legs
trait and then turn into flippers?
In the deepest fossil layer, this animal started out having long front legs, which is a dominant
trait. In the next fossil layer closest to the surface, some of these types of animals have long
front legs and some have short front legs, which was the recessive trait. In the fossil layer after
that, the animal gets the genes to give it front flipper and get rid of legs altogether. It then
continues to be a recessive trait and stay with the flippers in the front. When this animal ad long
front legs, the genotype was Ff or FF for all of the animals, but FF genotypes were rare so most
of the animals had Ff. In the next layer closer to the surface, some of the animals had the
genotype Ff and some had the genotype ff. In the last two layers closest to the surface, the
animal has flippers and continues to have flippers permanently. Something must have happened
to the gene in the animal to make the front legs turn into flipper altogether. It could have been
that the gene that controlled whether the animal had long front legs, short front legs or flippers
disappeared and forced the animal to have a third option, flippers. There was a 75% chance of
the animal getting a long front legs and a 25% chance of the animal getting short front legs.
There s no way the animal could have flippers, unless something happened to the genes that
controlled the front legs, and it caused the animal to get flippers permanently. This animal lived
in an environment that had good-sized trees, small shrubs, and small creeks. Not much sunlight
got though to him to cause a mutation in his DNA. No chemicals, cigarette smoke, drugs,
pollution or radiation got to him to cause something to change the way he looked. When his
environment changed in the next fossil layer, he started changing. When more sunlight reached
him, he had already had his genes read the DNA to tell him what to look like. So when the
environment changed from medium trees, smaller shrubs, and small creeks to taller grasses,
smaller shrubs and swamps, more sunlight is reaching this animal through water and because
there are no trees. When the environment then changed to taller grasses, shallow ponds and
swampy land, even more sunlight is hitting the animal. But in the fossil layer before this one,
half the animals have the same genes as in the first layer, but now some of their offspring have
different genes from when the excessive sunlight hit them to cause a change in the DNA. When
the animals in the first layer had already gotten their genes, only the mutated genes show up in
their children. So when even more sunlight reaches their offspring, it causes the changes to
continue. And because the changes happened, if it made living in that environment worse, the
numbers of that type of animal would decrease. But if it was an advantage, the number would
increases, because the types of animal would live longer to have more offspring. The flippers
Amanda Barry, Colette Gilbert, Jack Hobbie
Part 1 of Performance Assessment Task
would cause an animal to be in the water, so when the environment caused the animal to be in
more water, more sunlight would filter in and cause a change in the DNA.
How is it possible for the dominant long back legs trait to change to a recessive short back legs
trait and then disappear completely?
In the following pictures it shows that the back legs are dominant and started out in the earliest
layer of being fossilized, which means the genotype is Ll. In the next layer of fossils, it stays the
same, because none of the genotypes changed. In the third fossil layer, the long back legs
(dominant), became short back legs (recessive.) And in the closest layer to the top, disappeared
completely. If in the deepest layer, the genotype were LL, then there would be no possibility ever
of the animal ever evolving. Then the only possibilities would be to have long back legs, so Ll is
the reason the back legs became short and then disappeared entirely. It then became short back
legs and then disappeared completely. There is some reason why the back legs disappeared
altogether. It could’ve just been because it evolved of the chromosome where in the DNA it
described the back legs and something happened to it to make it disappear entirely. In the
punnett squares shown below, there is a 75% chance of the animal having long front legs and a
25% chance of the animal would have short front legs. Something must have happened to the
genes that controlled the back legs, because in the punnett squares, there is no way for the
animals to get no back legs at all unless the gene dies or was changed to make the animal have
long back legs, then short back legs and then no back legs at all. The animals in this
environment start out having dominant back legs, and have long back legs for two more fossil
layers. The environment doesn’t have an effect on the beck legs DNA until the environment
changes to taller grasses, small ponds and swampy. Because the sunlight is what causes a change
in the DNA and since the animal can have back legs in watery environments, there is no change.
Once that generation of animals has kids, the mutation shows up in the offspring to get short
back legs. IN the next fossil layer, the animal has no back legs at all; his environment is now
deep lakes and many aquatic plants. Because he lives in water, (most of the time or all the time),
he doesn’t need back legs and now has sunlight on him all the time. His DNA could still change
because there is even more sunlight that could cause his genes to change, but only show up in
the offspring.
Amanda Barry, Colette Gilbert, Jack Hobbie
Part 2 of Performance Assessment Task
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?
Starts as Ff x Ff, Ff x Ff These are all 75% to have no fluke, 25% for a fluke EVERY
SINGLE TIME. But due to it being random it turned out equaling ff so it can now
only permanently be fluke. So from then on only can be ff. (Jottings)
(My real explanation includes jottings)
In the deepest layer, the animal starts out having no flukes Ff. In the next layer, closest to the
top; the animal still has no flukes. When some of the animals have different genotypes, the no
flukes. These are all 75% to have no fluke, 25% for a fluke EVERY SINGLE TIME. But due to it
being random, the offspring all have the same chance of having no flukes or flukes. It turned out
equaling ff so it can now only permanently be fluke. So from then on only can be ff, which proves
that it is possible for the flukes to start out being dominant and no flukes, turn to flukes, which
was the recessive trait in this specific animal.