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Unit 4
KEY
Name _________________________
How Organisms Evolve and Survive on Earth
Evolution
Evolution is defined as “heritable genetic changes seen in a population over time”…
Populations
1. Evolution refers to ____________________,
not individuals
2. The changes must be passed on to the next generation (be inherited)
DNA & Protein Comparisons
The Best Evidence to Determine Evolutionary Relationships
The structure of DNA is common to all life, and living organisms all use the same genetic code (the
same combination of 3 bases – ATG, for example – code for the same amino acid in all organisms – a
tree, a mushroom, a rabbit, or a human)
Scientists look at similarity between DNA sequences (the order of bases that make up genes) to
fewer
determine relatedness. The more closely two species are related, the _____________
differences
there are in their genes
Remember - DNA codes for building proteins (chains of amino acids). Some proteins are
common to many different species, and they change very little over time because they play a crucial role
oxygen
in cell function – so mutations would be detrimental (bad). Hemoglobin is the ______________transporting blood protein found in most vertebrates (animals with backbones). By studying the amino
acid sequences of hemoglobin from different animals, scientists can determine evolutionary
relationships.
increases
As genetic relatedness decreases, the number of amino acid difference _________________.
For
0
example, there are ______
amino acid differences between humans and chimpanzees, indicating they
67
“recently” (in geologic time) shared a common ancestor. Humans and frogs have ______
amino
acid differences, indicating they had a common ancestor a very long time ago.
Once relationships between species are
“figured out”, scientists can make
“evolutionary trees”, like this one:
All of the organisms shown shared a
common ancestor a long time ago. The
branches show the last point in which the
organism shared a common ancestor with the
other organisms.
So, of the living organisms shown,
marsupials and placental mammals would be
the most closely related because they are the
last to “branch away from each other”.
Species
Once similar organisms are put into groups, how do you know if they are the same species? Like these
rabbits….are they the same species of rabbit?
1. Remember, a species is a group of similar organisms that, in nature, will
reproduce
successfully _________________
(produce fertile offspring).So,
obviously, we could breed these rabbits to see if they produce
fertile offspring. If they do, then they are, by definition, the same
species of rabbit.
2. We can observe them in their natural habitat to determine whether or
niche
not they share the same ____________.
(a niche is how they live and
survive in their habitat) Since no two species can occupy the same niche
at the same time, if they do, they must be the same species (even though
they don’t look very much the same).
3. We could also take DNA samples from each one, and see how many
genes they have in common. The more common genes, the
more closely related they are. We could also examine protein
structure (amino acid sequences) to determine how closely related they
are.
4. We could also compare common body structures (anatomy), growth and
development from an embryo, etc.
But, again our best evidence will come from examining DNA and/or
protein structure.
Review:
12. Common Ancestors & Species
What evidence would scientists used to
determine that the Arctic fox and the raccoon
dog share a common ancestor?
Scientists could compare the following between
the two species:
 Anatomical structures
 DNA sequences of genes
 Amino acid sequences of proteins
The more anatomical structures, nucleotide, and
amino acid sequences that the two species have
in common, the more recent the common
ancestor between the two.
Looking at the evolutionary tree, what is more closely related to a dog – a coyote or a golden
jackal? How can you tell?
The dog is more closely related to the coyote than to the golden jackal. On the evolutionary tree,
the branches which connect the dog and coyote diverge from a common ancestor at a more recent
time than do the branches that connect the dog and golden jacket.
Imagine that you were in Canada and found an animal that you think is a gray fox. Another
similar looking fox was found in Northern California. Describe two ways that you could test to
determine if they are the same species of fox, and what each test would “tell you”.
Test that could be used to determine if the
two foxes are of the same species:
Breeding the two foxes to each other
What the test outcome would show if the
two foxes were of the same species.
The offspring produced would be fertile.
Observing how the foxes make their living
If they have the same niche
Gene comparison
If their genes are very, very, very similar.
Amino acid sequence comparison
If the sequence of the amino acids in selected
proteins are very, very, very similar.
Most frogs require habitat in both terrestrial (land) and aquatic environments. Unlike your skin that
serves as a strong barrier to most chemicals, pathogens, viruses, etc., a frog’s skin is thin and very
permeable (materials can easily pass through it). Because of this, toxic chemicals that enter their
environment are easily absorbed through a frog’s skin. Mutations can occur in frogs that are exposed to
chemicals from farm or factory run-off, sewage run-off, etc. Describe one example of a type of
change in a molecule that would result in a mutation.
Mutagens can disrupt DNA replication. This disruption may result in one of the following types of
mutations occurring in a DNA sequence:
a) a nucleotide substitution
b) a nucleotide deletion
c) a nucleotide insertion
Amphibians were the first vertebrates to live on land; this “movement” began about 360 million years
ago. Today, there are many different species of frogs, toads, and salamanders, but they all share a
common ancestor. Describe one example of evidence that would support this conclusion.
1) Comparative anatomy: Frogs, toads, and salamanders have shared, homologous
characteristics, like all having backbones and four limbs, being cold-blooded, spending most of
their time in water, having permeable skin, not possessing scales, having gills at some point in
their lives, and going through metamorphosis.
2) Similarities in the nucleotide sequences of DNA
3) Similarities in the amino acid sequence of proteins.
____ COE: Worms in Action #3
Individual Variation within a Species
Even if organisms are of the same species, no two individual organisms are exactly the same. So what
causes the variation in members of the same species?

Sexual reproduction – because each organism is “created” by the combination of unique sperm
DNA with unique egg DNA, the offspring created has DNA that is different than even its “brothers
and sisters”. …each individual produced by sexual reproduction is unique. – this is genetic
variation.

Random mutations during the formation of egg or sperm also contribute to “unique” offspring.
This genetic variation gives some individuals in a population a survival advantage over other
individuals, so some individuals may be more likely to survive and reproduce and pass those genes on.
Sometimes environmental changes favor certain “variations”, or differences, in
individuals in a population. For example, if the temperature in a lake is gradually
increasing, individuals with genes that allow them to survive in the warming waters
will be the ones that more successfully produce offspring……so, over time, more and
more of the “warm water gene” will show up in the population.
niche
The genetic variation in this lake has most likely __________________
over time. Since only
those fish with genes suited for the warmer water survive and the fish with “colder water genes” can no
longer be found, there is less variety of “fish genes” in the lake.
Let’s say the two fish shown are of the same species and have survived the warming
waters. The “plump and round” fish is brown, and that skin color gene is dominant
(B); the “sleek and thin” fish is green which is recessive (b). The lake is full of green
vegetation, so the green fish are better able to hide from predators, which means
they have more reproductive success. In this lake, there are many more of green fish
than brown fish.
After a period of time, a certain parasite that is attracted to the green fish was
introduced into this lake ecosystem. The green fish became sick and started to die off.
Since the brown fish are easy bait for hungry predators, this entire species could be
driven to extinction. If that occurred, the predator populations could become
endangered as well, since they would be lacking adequate food.
Now, imagine that local factory dumped chemicals into the lake that killed the green vegetation,
leaving only the sandy, rocky bottom visible. In this situation, the green fish would become easy
targets for predators, and the populations of brown fish would most likely increase since they can
“hide”. So, over time, the lake would be dominated by brown fish….and the number of recessive alleles
(bb) expressed in the population would be dramatically reduced.
Environmental changes can have a huge impact on the genetic diversity in any ecosystem.
Review:
13. Genetic Variation & Survival
Jackrabbits all have the same general appearance, but no two jack
rabbits look exactly the same. What causes this variation in jackrabbits…..and how does it cause variation?
Variation in jackrabbits is due to the process of sexual reproduction. During
gamete production, mutations that occur during DNA replication cause slight
differences in the DNA sequences of each egg and sperm. In addition,
independent assortment and crossing over shuffle existing alleles into new
combinations, making each gamete truly unique.
Variation is also based on how these differences are expressed. For example,
assuming jackrabbits have two alleles that code for fur color (dark brown fur
and light brown fur)—the following inheritance patterns are possible:
 Complete dominance—dark brown (BB or Bb); light brown (bb)
 Incomplete dominance—dark brown (B1B1); medium brown (B1B2);
light brown (B2B2).
 Codominance—dark brown (B1B1); patches of dark and light brown
(B1B2); light brown (B2B2).
Jackrabbits have many adaptations that make it possible for them to survive in their habitat. A
few unique adaptations are:
1. They have long ears and long limbs which help them release heat. This keeps their body
temperature in balance (homeostasis) making it possible for them to survive in a hot
desert-like habitat.
2. They can run about 40 miles per hour to escape predators.
3. They have eyes high on their head that are placed towards the side; this, along with the
fact that their head is slightly flat, allows them to see almost 360 degrees (a full circle)
which helps them spot predators.
Imagine, in a litter of jackrabbits, that 1 of the babies has legs and ears that are slightly longer
than average. How might this variation allow this rabbit to survive and reproduce in its
environment?
The jackrabbit with the longer ears may be able to hear approaching predators,
like coyotes, better than those with shorter ears. The longer legs may enable the
jackrabbit to run faster from predators than those with shorter legs. Both of
these traits may help keep the jackrabbit from being eaten, and thus survive long
enough to reproduce.
Imagine that the jackrabbit’s natural habitat is gradually getting warmer; summer
temperatures used to average 1050F, now it is not unusual to have days as hot as 1150F. How
could natural selection (“survival of the fittest”) affect the population of jackrabbits over
time? The long ears of jackrabbits are also used to radiate out body heat. Jackrabbits ears are thin and full
of blood vessels. When temperatures start to rise, jackrabbits can regulate the flow of blood through
their ears by dilating their blood vessels. This allows heat to escape into the air around the
jackrabbit, cooling it off in the process. Those jackrabbits better able to cool their bodies and retain
water during hot days are more likely to survive and reproduce than those who are not as well
adapted. These adaptive traits that allow jackrabbits to cope with the heat will be passed on to
offspring. Over time, these traits will become more prevalent in the population.
How do you think this warming could affect the genetic variability within the population of
jackrabbits in this ecosystem?
Evolution is a slow process. If the temperature of the environment changes slowly (thousands to
millions of years), new traits may emerge over time that will help jackrabbits better adapt. However,
the rate of current temperature increases due to global warming could outpace jackrabbit evolution.
This would result in a decrease in the genetic variability within the jackrabbit population and may
even lead to the extinction of the species.
Miller’s pond is located about ½-mile downstream from a
large farming operation. Although these farmers carefully
monitor the use of fertilizers and other chemicals, over time,
small but continuous quantities of various fertilizers have
made their way into the groundwater and streams leading to
Miller’s pond. With the addition of fertilizers, plant and algae
populations in and around the pond have increased
significantly in the past 50 years. The pH of the pond has
also gradually decreased, making the water more acidic than
it used to be.
Describe how, over time due to this environmental
change, natural selection has most likely impacted a population in Miller’s pond.
1) Most freshwater ponds have a pH between 6 and 8. Low pH can have an effect on reproduction (eggs
are unable to hatch) and food sources (insect die-0ff). If the pH drops too low over time, then some
amphibians and fish species will not be able to cope and their populations will decrease (selected
against). Those species that are able survive will reproduce and increase in numbers (selected for). For
example, bass die off when pH drops to 5.5. Trout die off at pH 5.0 and perch die off at pH 4.5.
2) Large algal blooms can occur due to high fertilizer run-off. When the algae die, they fall to the bottom of
the pond. Bacteria decomposing the dead algae use up most of the oxygen in the pond. As dissolved
oxygen levels drop below 14 mg/L, fish like salmon and trout will die off first (11-13 mg/L), followed by
bass and bluegill (9-10 mg/L), and then carp, perch, and walleye respectively (5-8 mg/L).
Predict how a changing pH could affect genetic variability of a population in this ecosystem. Describe a
reason for your prediction.
Every population of a species has genetic variability. Some species populations have a lot of variability (like
dogs), others not so much (like cheetahs). Those species with high variability within a population have a
greater probability of its members possessing traits that allow them to cope with a changing environment.
As the environment changes, individuals with traits that allow them to survive and reproduce will become
more numerous in the population over time. Individuals with non-adaptive traits will become less
numerous.
For example, in a population of bass there will be individuals who can cope with stress better than others.
When pH levels change, bass become stressed and this stress weakens their immune system. Bass with
weakened immune systems are more susceptible to disease and may die off. Bass which don’t become as
easily stressed will have a stronger immune system, enabling them to survive and reproduce. The result of
changing pH levels will result in a decrease in the genetic variability within the bass population.
Some chemicals can cause genetic mutations in organisms. These mutations can change the genetic
variability in a population. Given the following DNA sequence, describe two types of genetic mutations
that could occur.
DNA: TAC GGT CCA
In your description, be sure to:
 Identify two types of genetic mutations
 For each type, show what the new DNA sequence might be
One Type:
Substitution: A nucleotide (base) in the original sequence has been substituted with a different nucleotide.
Example: Original strand TAC GGT CCA
In this case, the 4th base (G) has been replaced with an A.
Mutant strand TAC AGT CCA
Another Type:
Deletion: A nucleotide (base) in the original sequence has been deleted.
Example: Original strand TAC GGT CCA
In this case, the 4th base (G) has been deleted.
Mutant strand TAC GTC CA
Describe how it is possible that a genetic mutation could benefit a population of organisms.
In your description, be sure to:
 Identify a changed caused by a mutation that could benefit a population.
 Describe how that change could benefit the population




A mutation in a gene that codes for the slime coating on the pathogenic bacteria that causes cholera
could make the slime stickier. This might help cholera bacteria attach to intestinal membranes better
so that it can deliver its toxin that causes severe diarrhea.
A mutation in the gene of a house spider that allows for the production of an enzyme that can
breakdown a particular insecticide, like Raid ©. This helps the spider survive the application of the
insecticide. The surviving spider can reproduce and pass down the mutant gene to its offspring.
An antelope born with longer legs that enables it to outrun wolves and coyotes. This will help the
antelope survive and reproduce; passing down the genes involved in long-leg production to some its
offspring.
A mouse that inherits a mutant gene which codes for melanin (a pigment) production develops a
darker coat color than other mice in the population. The darker coat provides better camouflage than
the lighter-colored coats. This helps the mouse avoid predators and survive long enough to reproduce.
Miller’s pond is home to a particular species of frog. Some of the frogs have a greenish skin color, while
others have more of a brown skin color. The gene for brown skin (B) is dominant over the gene for
green skin (b). Birds and snakes found around the pond are predators to this species of frog.
Over the years, it is becoming increasingly difficult to find a brown-skinned frog around Miller’s pond.
Describe what could have cause the green-skinned population to increase over time.
An increase in fertilizer run-off into the pond could have indirectly caused the decline in brownskinned frogs. Increased levels of nitrates in the water create algal blooms and lush vegetation. In this
green background, green-skinned frogs would be well camouflaged against predators like birds and
snakes. Green-skinned frogs would be more apt to survive and reproduce, increasing their numbers.
Brown-skinned frogs would not fare as well and be eaten at higher rates. This would result in a drop in
the numbers of brown-skinned frogs in the population.
A certain disease carrying insect is more attracted to the green colored skin, and has been infecting
them with a deadly virus. The populations of green-skinned frogs are decreasing dramatically.
Describe the effects on the brown-skinned frog populations and frog predator populations over time if
this vector (insect) cannot be controlled.
In your description, be sure to:
 Identify an effect on the brown-skinned frog population over time and an effect on the frog
predator population over time
 Describe a reason for each effect.
Effect on brown-skinned frog population:
The population of the brown-skinned frogs would increase since they are not competing with the
green-skin frogs for resources, like food, shelter, and mates.
Effect on frog predator populations:
The frog predator populations will increase. This is because as the brown-skinned frog population
increases, there will be more brown-skinned frogs for the predators to eat. The brown-skinned frogs
are more easily seen against the green vegetation, which makes them easier for the predators to catch.
After 75 years the farming operation near Miller’s pond was sold. The new owners are not farming, but
are attempting to restore the land to its original “pre-farming condition”. For this reason, fertilizers
and chemicals are no longer being used, and chemical run-off is no longer a concern. Without fertilizer
run-off, the population growth of plants and other photosynthetic organisms in and around the pond
has decreased. The pond no longer has its lush green appearance. Describe the effect of this change on
the frog populations over time.
In your description, be sure to:
 Describe the effect on the frog population over time
 Describe a reason for that effect
With a decrease in green vegetation in the pond, the brown-skinned frogs will no longer be at a
disadvantage regarding camouflage. There numbers should increase as more of them survive and
reproduce.
Conversely, the green-skinned frogs will be more visible in areas where there is little or no vegetation
(like on a sandy shore or in open water). The green-skinned frog population should decrease as more
of them will be spotted and eaten by predators.
____ COE: “Carbon Matters #3”
____ COE: “It’s in the Genes #3”
____ COE: “Bear Crossing #2”