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The Making of the Fittest: The Birth and Death of
Genes
Icefish adaptations and How novel icefish genes
can improve human health
Introduction:
Approximately 40 million years ago, Antarctica separated from South America connecting the Atlantic and
Pacific oceans. Over the next 13 million years or so, the gap, called Drake Passage, widened causing wind
and ocean current patterns to shift and the water temperature to drop. The temperature of the Southern Ocean
gradually decreased to it’s present day -1.9ºC (30ºF). The permanent icecap that covers Antarctica also formed
at this time. Most fish species in the region were unable to tolerate the environmental changes and died out.
One group of fish, however, the notothenioids, not only survived the changes, but they have come to thrive in
the harsh Antarctic environment. Notothenioids have been successful not because they keep out more
aggressive fish species, but because they are the only fish that can survive in the freezing Antarctic waters.
Icefish are a group of fish that belong to the Notothenioid suborder that lives in the most extreme Antarctic
environments. Just how is it that icefish are able to tolerate the extreme conditions in which they live? What
adaptations do they possess?
Antifreeze Experiment:
One of the key notothenioid adaptations is their ability to make antifreeze proteins. Antifreeze proteins enable
them to tolerate conditions that would cause other fish to freeze solid. The antifreeze proteins work by binding
with ice crystals at the molecular level and preventing them from growing. Based on genetic evidence,
scientists think the antifreeze adaptation evolved between 5 million and 14 million years ago. This is about the
same time as the geological evidence for the estimated time of the freezing of the Antarctic Ocean (10–14
million years ago), and the time notothenioid group is thought to have expanded (7–15 million years ago).
Since early notothenioids invaded the Antarctic, more than 120 species have evolved. Each occupies a
different niche, or role in the ecosystem. In this experiment, you will use simple materials to model the function
of the notothenioid antifreeze protein.
Procedure:
1. Fill the polystyrene cup with crushed ice. Add 1 teaspoon of salt to the cup of ice and stir to mix the
contents.
2. Add antifreeze solution to one test tube so that it is approximately 1/3 full.
3. Add the same amount of the water to a different test tube.
4. Measure the temperature of the ice and salt mixture in the cup and then the contents of each test tube.
Record your measurements below.
______ ice and salt mixture
______fresh water
______ water with antifreeze
5. Place the test tubes in the cup of crushed ice.
6. Watch the short film on the Birth and Death of Genes.
7. Measure the temperature of the ice and salt mixture in the cup and then the contents of each test tube.
Record your measurements below.
______ ice and salt mixture
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______fresh water
______ water with antifreeze
Icefish adaptations: Student handout
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The Making of the Fittest: The Birth and Death of Genes
8. It will take time to see if ice crystals form in the fresh water and if the antifreeze prevents the formation of
ice crystals in the other tube. While waiting, watch the film The Making of the Fittest: the Birth and Death of
Genes. As you watch:
a. List other icefish adaptations mentioned in the film.
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b. Record how scientists think the antifreeze gene evolved.
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9. After watching the film, check the test tubes to see what has happened.
a. Describe any differences you observe between the two test tubes.
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b. Form a hypothesis to explain how ice crystals interfere with the flow of blood and damage tissues.
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Questions:
1. Notothenioid fish evolved about 25 million years ago, during the time the Southern Ocean was cooling.
Icefish, a member of the notothenioid family, appeared much later after the Southern Ocean had cooled
significantly.
a. Explain why the evolution of the antifreeze gene was essential to the survival of notothenioid fish as the
Southern Ocean cooled.
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Icefish adaptations: Student handout
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The Making of the Fittest: The Birth and Death of Genes
b. The globin gene, which codes for hemoglobin, is no longer functional in icefish. Yet, this gene is very
important in almost every other fish species. Explain how icefish are able to survive without the globin gene
and how it came to be eliminated from the icefish genome.
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2.Similar to antifreeze production, several of the adaptations described in the film have to do with icefish
blood. Select one of these adaptations and explain how it has enabled icefish to survive in icy water.
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3.Explain what is meant by the following, “Natural selection, which is not random, determines which chance
events (mutations) are retained.”
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The Making of the Fittest: The Birth and Death of Genes
How novel icefish genes can improve human health
Introduction:
Icefish are among the only fish that thrive in the oxygen-rich cold waters surrounding Antarctica. They have
evolved a set of unique adaptations that enable them to survive in an environment that would be deadly to
other fish. Several of these adaptations are associated with major health problems in humans. Can icefish help
us understand human disease? Scientists certainly think so. The novel genes responsible for the icefish’s
unique set of traits might lead to new treatments for common diseases such as anemia and osteoporosis.
Questions:
Read the passage below and answer Questions 1–3.
Icefish and Anemia: A person is diagnosed as anemic if their blood lacks an adequate number healthy red
blood cells or if their red blood cells are deficient in hemoglobin. Both conditions result in an inadequate
amount of oxygen reaching the cells. Many parts of the body help make red blood cells, though most of the
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Icefish adaptations: Student handout
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The Making of the Fittest: The Birth and Death of Genes
work is done in the bone marrow. Once they enter the bloodstream, healthy red blood cells circulate for
between 90 and 120 days before being broken down and recycled by the body.
There are more than 400 different types of anemia. These can be divided into three basic groups. Anemias
caused by:
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defective or decreased red blood cell production;
red blood cell destruction;
blood loss.
Icefish could provide information that will help with treatment and possible cures for the first two types of
human anemias. For example, scientists have compared the genomes of icefish, which lack red blood cells, to
that of their close relatives that have red blood cells. The comparison led scientists to a novel gene, named
bloodthirsty (bty), that is expressed in icefish relatives but not in icefish. Scientists are investigating the role of
the bty gene in red blood cell formation and destruction.
1. Using the list of adaptations you recorded during the film, (a) list the icefish traits would be of direct interest
to researchers investigating anemia in humans, and
(b) explain how each trait is related to anemia.
a. Traits:
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b. Explanations:
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2. Below is a chart of icefish adaptations not mentioned in the film. Based on your knowledge of anatomy and
physiology, place a check mark on the line in front of the three adaptations that MOST directly play a role in
assuring that icefish tissues receive an adequate amount of oxygen.
Icefish Adaptations not mentioned in film
___ enzyme molecules that work at low temperatures
___ low blood pressure
___ large heart
___ large, bulging eyes with lots of rods
___ abundance of lipids distributed throughout the body
___ wide blood vessels
___ large volume of blood
___ no swim bladder
3. Write a paragraph that explains how the adaptations you selected enable icefish tissues to receive an
adequate amount of oxygen.
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Icefish adaptations: Student handout
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The Making of the Fittest: The Birth and Death of Genes
Read the passage below and answer Question 4.
Icefish and Osteoporosis: Another adaptation that has piqued the interest of researchers is the light, thin
skeleton of icefish. Essentially, icefish have reduced their bone density. Just how did icefish come to decrease
the mineralization of their bones and to replace bone with connective tissue?
About 34 million years ago, icefish lived on the ocean floor. They were so well adapted to life on the ocean
bottom that they lost their swim bladder. In other fish, the swim bladder regulates buoyancy making it possible
for them to move up and down in the water column. When the temperature of the ocean surrounding Antarctica
began to drop, other fish species either died out or migrated to warmer regions. This left the bottom-dwelling
icefish with new niches to exploit. The problem was, without swim bladders, they could not get to food that was
available up in the water column. Evolution solved this problem! Over a period of approximately 4 million years,
icefish shed bone density thus increasing their buoyancy. This trait mimics the human condition osteopenia,
which is a lower than normal bone mineral density. In the United States osteopenia affects 34 million women
and 12 million men. Osteopenia often leads to osteoporosis, which is a disease characterized by bone
deterioration and an increased susceptibility to bone breaks and fractures.
4. Researchers have discovered that the demineralization of icefish skeletons is achieved through a change in
genetic timing. Genes that regulate bone growth are switched on for only a brief period of time. Genes that
build cartilage are active for a much longer period of time.
Explain how an understanding of the evolution of the demineralization of the icefish skeleton might help
scientists find an effective treatment or cure for osteoporosis.
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Author:
Mary Colvard
Cobleskill-Richmondville High School (retired)
Deposit, New York
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Icefish adaptations: Student handout
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