Download acj.part1--SCIENCE - Grade 8 Learning from the Fossil Record

Amanda Barry, Colette Gilbert, Jack Hobbie
Part 1 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 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 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.
 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
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.
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 short fat tail
didn’t have the genotypes of Tt, then there would be possibility of having a new type of tail, short
and fat or changing to no tail or any other characteristic a tail could have. 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 to permanently, to keep having the genotype tt. If the animal started out having a genotype
that was TT, than having a skinny tail in the beginning, never would have been possible. There is
a 50% chance of the aniaml getting a long skinny tail, (recessive – tt) and a 50% chance of the
animal getting a short fat tail, (dominant-Tt). Everytime there is an offspring born, there is a
50% chance of either, and every time, it is random so it could change every single time.
Amanda Barry, Colette Gilbert, Jack Hobbie
Part 1 of Performance Assessment Task
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 for all of the animals. 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 lage. There s no way the animal could have flippers, unless something happened to
the the genes that controlled the front legs, and it caused the animal to get flippers permanently.
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
animale to get no back legs at all unless the gene dies or was changed to make the animal have
long back legs, then hsort back legs and then no back legs at all.
Amanda Barry, Colette Gilbert, Jack Hobbie
Part 1 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.