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Science 11th grade
LEARNING UNIT
how do we transform the
planet?
S/K
Language
Socio cultural context of
the LO
Curricular axis
Standard competencies
Background Knowledge
English Review topic
Vocabulary box
LEARNING OBJECT
What is genetic drift?
 Define genotype and phenotype characteristics.
 Explain the concept of allelic frequency.
 Use the Hardy-Weinberg equation to calculate the
change of allelic frequencies in a population.
 Investigate the base of the stochasticity concept.
 Compare the impact of genetic drift with natural selection.
 Find examples of founder and bottleneck effects.
English
Colombia
Living Environment
Explain biologic diversity as a consequence of environmental
and genetic changes; and dynamic relationships within
ecosystems.
Students must understand ecologic concepts about
individuals, populations, communities, and ecosystems.
Additionally, basic knowledge about genetics: DNA
composition and properties, heritage, and process of
character transmission.
Use of That vs Which, what situations call for each
Hunter-gatherer: A member of a culture in which food is
obtained by hunting, fishing, and foraging rather than by
agriculture or animal husbandry.
Environment: The conditions that surround someone or
something. The conditions and influences that affect the
growth, health, progress, etc., of someone or something.
The environment: the natural world.
Equilibrium: A state in which opposing forces or actions are
balanced so that one is not stronger or greater than the
other. A state of emotional balance or calmness.
Name: ___________________________________________________________
Grade: ___________________________________________________________
INTRODUCTION
Simona: Have you heard about “chuckwalla”?
Patricio: Is it a new reggaeton singer?
Simona: Hahaha. No, it is a herbivore lizard, which lives in the United States and
Mexico. Its scientific name is Sauromalus obesus.
Patricio: With that name, it must be huge.
Simona: Well, it actually grows throughout its life; however, it doesn’t grow more
than a few centimeters. And the ones that live in higher altitudes are bigger than
those in lower altitudes.
Patricio: Why? The ones that eat more are obesus. Hahaha.
Simona: You guessed it! The ones in higher altitudes have more food available
than those in lower altitudes. An experiment was conducted to see if the growth
had to do with available food or genetic differences.
Patricio: How? Who conducted the experiment?
Simona: A scientists, Christopher Tracy. He took baby lizards from different
altitudes and placed them all in a similar habitat recreated in his lab.
Patricio: With lights, rocks, and food?
Simona: Exactly, the food was available at all times so it wouldn’t limit their
growth.
Patricio: And, what happened?
Simona: All lizards grew just fine, but the ones from higher altitudes grew more.
Patricio: And what does that mean?
Simona: What determines the growth of the lizards is not the food, but the allelic
frequencies of the population.
Patricio: Allelic frequencies? what is that?
Figure. Chuckwalla. One of the species studied genetically to find out why there is a difference in
the specie’s morphology.
OBJECTIVES
Throughout this section you will be able to:
1. To evaluate the numeric interpretation of the evolution theories of all living
creatures.
2. To recognize the use of the Hardy-Weinberg equation to obtain biologic
information.
3. To produce written texts to explain the importance of numeric calculations
in science.
ACTIVITY ONE
Skill 1: Define phenotypic and genotypic characteristics.
Skill 2: Explain the concept of allelic frequency.
GENETIC PRINCIPLES
The research of naturalists and geologist Charles Darwin (1809-1882), and the
scientists and monk Gregor Mendel (1822-1884), revolutionized the world of
biology. With the theory of natural selection and Mendelian biology, the modern
study of evolution was born.
Mendelian genetics state that an individual’s characteristics are passed down from
parents to offspring in the form of genes, which can be understood as separate
information packets. Mendel determined that genes have alternative forms, known
as alleles.
In his experiments, Mendel worked with alleles such as smooth seeds compared to
course seeds, or tall plants compared to short plants. He observed that there are
dominant alleles, which manifest their phenotype in heterozygosis and recessive
alleles, which manifest their phenotype only in homozygosis.
Mendel also introduced the difference between phenotype and genotype. The
genotype is the genetic constitution of an organism, meaning the group of genes
that an individual inherits from its parents. This does not vary throughout its life,
independent of its environment.
On the other hand, the phenotype is the group of observable external
characteristics of an individual. The phenotype is produced by the effects of the
combination of genes and environment.
Experiments conducted with plants link phenotypic and genotypic variation. These
have illustrated, for example, that there is a link between precipitation and the size
of a plant. The success of a plant depends, aside from its genetic composition, on
its morphology (Molles, 2006).
Example:
It is possible to see how the interaction of genes affects an individual’s phenotype
in the color of Labrador dogs. Labradors have three basic colors: black, yellow, and
brown.
Genes located in two fixed places in the chromosomes determine these colors.
The general proportion of black Labradors is 56%, yellow is 25%, and brown is
19% (FCV, UNNE, 2011).
Figure. Labradors. Represent an example of change in phenotype, from the
genotype.
ALLELIC FREQUENCY
When geneticists began to understand the laws of heritage and the changes
produced by mutations of genetic variability, they wanted to know how that
variability behaved through time, meaning, which was the allelic frequency of a
population.
Allelic frequency or gene frequency is the proportion of each allele present in a
specific population. Allelic frequency is the characteristic that has to be taken into
account in order to understand how genes are transmitted within a population. It
has been proven that natural populations have a wide spectrum of genetic
variations.
The mathematician Hardy and the doctor Weinberg asked themselves if the
proportion of two existing alleles for the same characteristic would modify from
generation to generation after sexual reproduction. In 1908 they found the answer
and demonstrated that resulting combinations after reproduction in generations of
diploid organisms, do not produce changes in the general composition of the gene
pool (Curtis et al., 2007).
The Hardy-Weinberg Equilibrium states that sexual reproduction does not
reduce the gene frequency of a population through generations. It stays constant if
the following conditions are met.
•
Absence of mutations.
•
Absence of immigration or individual displacement to the interior of the
population.
•
Absence of migration or displacement of individuals of a population.
•
Population must be infinitely large.
•
There must be random mating.
•
Natural selection does not affect alleles being considered (Curtis et al.,
2007).
If these previous characteristics were not present in given environments, the
frequency of alleles in a population would not change from a generation to the
next. Meaning, if a gene process alleles A and a, these would not change, nor the
frequency of the three possible genotypes: AA, Aa, aa. Therefore the gene pool
would remain in equilibrium.
Learning Activity
This activity will help you learn concepts related to phenotype, genotype, and allelic
frequency. Match the concept with its meaning and corresponding characteristics.
Concepts: phenotype, genotype, and allelic frequency.
Table 1. Phenotype, genotype, and allelic frequency; meaning and characteristics.
Concept
Meaning
Group of observable characteristics of an
individual.
Group of genes an individual inherits from
its parents.
Proportion of each allele present in a
specific population.
Does not vary throughout lifespan,
independent of its environment.
Characteristic that should be taken in
consideration in order to understand how
genes are transmitted within a population.
A result of the combination between genes
and the environment.
It remains in equilibrium if there is no
mutations, immigration, migration, if it is a
large population, mating is random, and if
natural selection does not affect alleles.
Did you know that…?
One of the animal species most commonly used for genetic studies is the fruit fly,
Drosophila melanogaster. It has been used in labs since 1906, when Castle and
Woodworth from Harvard University introduced it as genetic material (Patil &
Biradar, 2011).
Currently, it is widely used in genetic labs all over the world; even NASA has used
it for outer space experiments.
Its importance is due to the fact that it is present and plentiful all over the world. Its
genome is well known, it is easy and economic to manipulate, it has a short
lifespan, it has a wide offspring production, it is a eukaryote with few
chromosomes, and shows many mutations manifested in phenotypic
characteristics (Escobar et al., 2004).
Figure. The fruit fly Drosophila represents one of the animal species most
commonly used in genetics.
ACTIVITY TWO
Skill 3: Use the Hardy-Weinberg equation to calculate the change of allelic
frequencies in a population.
HARDY-WEINBERG EQUATION
The Hardy-Weinberg equilibrium can be expressed mathematically through an
equation, which determines the intensity and the direction of change in the allelic
and genotypic frequencies:
Hardy-Weinberg equation
𝑝2 + 2𝑝𝑞 + 𝑞 2 = 1
Where:
p
: is the dominant allele frequency
q
: is the recessive allele frequency
2
p
: is the dominant homozygote frequency
q2 : is the recessive homozygote frequency
The sum of p and q must always be 1, meaning, the sum of both represents all
alleles of that gene, which is equivalent to 100% of its gene pool. Individuals in the
equation are assumed as homozygotes (Curtis et al., 2007).
Example:
Spider monkeys are widely found from Central to South America, including
Colombia. This species is in danger of extinction due to deforestation, the
destruction of its habitat.
Recent studies have showed an increase of albino monkeys due to an increase of
inbreeding due to the difficulty of the monkeys to travel to find other mates outside
of their family circle (Leaño, 2015).
The allelic frequency of this situation could be explained with the following
hypothetic situation:
In a population of 15 spider monkeys the dominant allele determines their black
color, and the recessive allele defines their white color and albinism. Each monkey
has both alleles, so they have a total of 30 alleles.
Supposing that the number of dominant alleles is 10, in order to know the
frequency of dominant alleles it is necessary to divide by the allele total:
10
= 0,33
30
And if the number of recessive alleles is 20, in order to know their frequency, it is
also necessary to divide by the allele total:
20
= 0,67
30
In conclusion, the recessive allele, which defines the white color, is more frequent
(67%) than the dominant (33%), which defines the black color.
Now, when these allelic frequencies are applied to the Hardy-Weinberg equation,
the result is 1. This is equivalent to 100% of the gene pool of that gene:
0,67
+0,67
0,332 + 2(0,33)
Figure. Spider monkeys. One with the dark color allele, and the other one, an
albino, with the recessive allele (Leaño, 2015).
Learning Activity
This activity will help you apply the Hardy-Weinberg equation to calculate the
change of allelic frequencies of the Asian ladybug Harmonia axyridis. This species
illustrates variations in their elytra color.
There are different varieties such as dominant homozygote genotype “signata”.
This variety has yellow elytra with black spots. The recessive homozygote
genotype “aulica” has elytra with black borders and two yellow or orange ovals.
Figure. Asian Ladybug Harmonia axyridis, important species in the study of allelic
frequencies. Represents color variations (Molles, 2006).
Suppose there is a population with 16 ladybugs. From these, 4 are aulica. Use the
Hardy-Weinberg equation to determine the percentage of the ladybug population,
which are heterozygote for the signata variety.
Now, solve the proposed situation:
What is the frequency of the recessive phenotype? Remember that this is obtained
from the division of recessive alleles by the allele total.
a.
b.
c.
d.
0,35 or 35%.
0,55 or 55%.
0,45 or 45%.
0,25 or 25%.
2.
What is the value for q? Find the square root q2.
a.
b.
c.
d.
0,3.
0,5.
0,5.
0,6.
3.
What is the value for p? Remember that the sum of both alleles is 1. So,
subtract 1 from the recessive allele frequency.
a.
b.
c.
d.
0,5.
0,4.
0,7.
0,3.
4.
What is the percentage of the heterozygote population? Remember to
calculate 2pk.
a.
b.
c.
d.
The 0,4 or 40% of the population.
The 0,5 or 50% of the population.
The 0,8 or 80% of the population.
The 0,3 or 30% of the population.
Very important…
A population, seen from a genetics point of view, is a group of organisms that mate
and share a genetic pool. In this manner, it is proven that evolution is the result of
the changes that occur in the composition of the genetic pool.
The evolution of a population depends on its genetics. In order for evolution to
occur, it is necessary for variations to develop within the organisms of a population.
These variations allow populations subjected to different conditions to be different.
There is no ideal variability, each population has its own and it changes
throughout time and space (Curtis et al., 2007).
Figure. the image represents a human population from a genetic point of view, in
which variations through genetic variability are illustrated.
Skill 4: investigate the concept of stochasticity.
Skill 5: compare the impact of genetic derivation with natural selection.
Skill 6: investigate examples of founder effect and bottleneck effect.
STOCHASTICITY
In a system where there were no disturbances, populations would grow to reach
load capacity. However, all ecosystems have disturbances and have the capacity
to function in these eventful and directionless situations. These situations are
known as stochasticity, there are three main types:
 Environmental Stochasticity: refers to spontaneous environmental
disturbances, caused by geologic, oceanographic, or meteorological
conditions such as earthquakes, eruptions, hurricanes, or drastic weather
changes. This type of stochasticity affects the survival and reproductive
probability of individuals. It has a strong impact on large as well as on
small communities, representing a risk of extinction for the species (Marín,
2019).
 Demographic Stochasticity: refers to changes in birth rate and mortality
suffered by individuals of a population. These are caused by eventualities,
such as an epidemic, or predation. This stochasticity affects the individuals
of a population in a different way, due to its effect being able to be
overcome in large populations. It has a major impact on small populations
(Marín, 2019).
 Genetic Sochasticity: refers to disturbances that occur on genetic flow,
which changes the genome of a population. This is the case of mutations,
gene flow, preferred mating, meaning not random, and genetic drift
(Molles, 2006).
GENETIC DRIFT AND NATURAL SELECTION
Genetic drift is a process that occurs mainly in small populations. In these, some
alleles can increase or decrease their frequency, or even disappear as a result of
chance.
For this reason, genetic drift is relevant in the evolutionary course of populations.
Nonetheless, its importance is relative when comparing it to the natural selection
process. This comparison is still an ongoing debate among scientists. (Curtis et al.,
2007).
Natural selection is the process that occurs when individuals with certain
characteristics have a survival and reproduction rate higher than other individuals.
These characteristics are hereditary to the offspring.
The genetic drift process is extremely important because without its variations,
evolution would not take place. Therefore, in order to generate different alleles,
eventful situations must take place, such as mutations and genetic recombination,
which can allow, or not, an individual to survive and reproduce.
The two main genetic drift situations, which demonstrate its importance, are: the
founder effect and the bottleneck effect.
The founder effect occurs when a new population is created from a small part of
another original population. This happens, for example, when part of a continental
population colonizes an island. The allelic frequencies of the new population could
be different from the original.
Figure. Graphically represents the founder effect, in which a new population is
created from a small part of an original population (Curtis et al., 2007).
Example of the founder effect:
Learning Activity
This activity will help to better understand concepts and characteristics related to
stochasticity, natural selection, and genetic drift. Complete the following
paragraphs with the corresponding concept:
1. As you know, ecosystems are subject to eventual and non-directional
disturbances known as stochasticity. Complete the following paragraphs about the
types of stochasticity.
The Zebu, Brahman Americano, breed has existed in Colombia for over 100 years.
It has been subjected to a continuous process of artificial selection, undergoing
endogenic reproduction and prone to the founder effect. Animal migration between
different farms and regions has homogenized the populations of the country. As a
result, this zebu breed is genetically different from all other zebu breeds in the
world (Novoa & Usaquén, 2006).
The other genetic drift situation is the bottleneck effect. This happens when the
number of individuals in a population is reduced drastically due to an event, which
has little or no relation to the usual pressures of natural selection. In this manner,
some alleles are eliminated, or in contrast they are found in excess (Curtis et al.,
2007).
Example of the bottleneck effect:
Between 1820 and 1880, the sea elephant of the northern California coasts was
almost hunted to extinction. Only close to 20 individuals remained. Since 1984, the
population has been protected and it has increased its numbers to more than
30,000 descendants from that small group.
Blood samples from sea elephant cubs show the large loss of genetic variability.
The disadvantage of not being carriers of different allelic combinations is that this
affects their probability, and that of their offspring, to reproduce and survive (Curtis
et al., 2007).
Figure. Represents one of the main cases of the bottleneck process, in which a
population is reduced drastically and there is an effect in some of their alleles.
a. Spontaneous situations caused by environmental disturbances such as
earthquakes, hurricanes, and drastic weather changes are characteristic of
___________________ stochasticity.
b. Mutations, gene flow, and
___________________ stochasticity.
genetic
drift
are
examples
of
2. Natural selection and genetic drift contribute significantly to the evolution of
populations. Complete the paragraph in order to describe the characteristics of
natural selection or genetic drift.
a. The ___________________ process occurs mainly in small
populations in which the allelic frequencies increase, decrease, or
disappear.
b. In the ___________________ process there is an interaction
between organisms and their environment. This is reflected in the
survival and reproduction of individuals with specific
characteristics
The following are examples of founder and bottleneck effects. Complete the
paragraphs with the corresponding process.
a. Cheetahs enjoyed a broad distribution in Africa, Eurasia and North America
until their population was diminished by the Pleistocene glacial period. From
the remaining population larger and stronger cheetahs emerged. This is an
example of ___________________.
b. In the Galapagos Islands there are some species of lemurs, which origin is
in Madagascar. It is unknown how the lemurs arrived on the island, but it is
speculated that it was on natural rafts. This is an example of
___________________.
Did you know that?
The Mlabri community is a hunter-gatherer group, which lives in the jungles of
Thailand, and it is apparently the only human community whose biologic founders
could be determined.
In 2005 DNA samples were taken from 300 people, from which 58 showed the
same exact genetic sequence. This had never been seen in any other human
population in the world, which suggests that this community was founded between
500 and 800 and it comes from a very small group of individuals (Oota et al.,
2005).
Figure. The Mlabri community is the only human community who knows its biologic
founder.
ABTRACT
What is phenotype and genotype?
Genotype is the genetic constitution of an organism. Phenotype is the group of
observable, external characteristics of an individual.
What is allelic frequency?
Allelic frequency is the proportion of each allele, present in a specific population. It
is the characteristic that should be considered to understand how genes are
transmitted in a population.
For what do you use the Hardy-Weinberg equation?
The Hardy-Weinberg equation is used to measure the intensity and direction of
change in the allelic and genotype frequencies.
What is stochasticity and what types are there?
Stochasticity, in biology, refers to disturbances, which occur in ecosystems. There
are three main types: environmental, demographic, and genetic.
What is the impact of genetic drift and natural selection in evolution?
Natural selection is the process that takes place when individuals with certain
characteristics have a higher survival and reproduction rate than other individuals.
It acts together with genetic drift, which changes allelic frequencies in populations.
In this manner, both represent an important role in evolution.
What is founder effect and bottleneck effect?
Founder effect and bottleneck effect are the two main genetic drift situations. The
first occurs when a new population is formed, from part of another population.
Bottleneck occurs when the number of individuals of a population is reduced
drastically due to a sporadic event.
HOMEWORK
The homework will help apply the Hardy-Weinberg equation and interpret the use
of its results in the health field. Get together with two other classmates and develop
the following stages.
Research Stage
For this stage, use different information sources such as the school library; if
possible consult with science or medical professionals.
 Research and list the genetic illnesses most common in Colombia.
 Choose one of those illnesses and find out the number of people who suffer
from it in Colombia.
 Research about the specific causes, the symptoms, the complications, its
treatment, and prevention, if it exists.
Hardy-Weinberg equation application stage
Take the number of people who suffer from the illness you chose and using the
equation, obtain the percentage of the population carriers of the allele that causes
the illness.
Documentation and promotion stage
In this stage you will write, in present time, a one-page report using the following
content.
 Describe the illness chosen.
 Include the percentage of carriers of the allele that causes the illness and
explain how you got the result from the equation.
 Write your conclusion explaining the importance of knowing the
characteristics of the illness you chose and the importance of the
mathematic tools used to find the incidence of the illness in the population.
 Include within the report the following words: genotype, phenotype, and
allelic frequency in bold lettering.
Share your document with your classmates and teacher. Keep in mind, which are
the most common genetic illnesses in Colombia from your results and those of
your classmates.
EVALUATION
1.
Match the following concepts related to the principles of genetics with the
corresponding meaning.
Concepts:






Gene
Dominant allele
Evolution
Recessive allele
Genotype
Phenotype
Concept
Meaning
Hereditary unit found in DNA.
An alternative form possible for the
same gene. It manifests its phenotype
in heterozygosis.
Process through which organisms in a
population change with time.
An alternative form possible for the
same gene. It manifests its phenotype
only in homozygosis.
The group of genes that an individual
inherits from its parents.
The group of external observable
characteristics of an individual.
Table. Concepts and meanings related to genetics with the corresponding
meanings.
2. Organize the following sentences related to the concept of allelic frequency.
Read them again to have the whole concept.
(specific population.) (allelic frequency) (of each allele) (present in a) (it is also
known as genetic frequency) (it is the proportion)
(characteristics to keep in mind) (allelic frequency is) (how do they transmit) (in
order to understand) (genes in a population.)
3. In this word search, look for the words needed to complete the necessary
conditions to maintain the equilibrium of genetic frequency in a population, also
known as Hardy-Weinberg equilibrium.
Conditions to maintain the Hardy-Weinberg equilibrium:
a. Random ______________.
b. Absence of______________.
c. Population infinitely ______________.
d. Absence of displacement of individuals to the interior of the population, or
absence of______________.
e. Absence of displacement outside or absence of ______________.
There is no effect on ______________ sample.
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4. Choose the following statements regarding the current situation of indigenous
communities in relation to megaprojects, as false (F), true (T), or true, but
miswritten (TM).
a. Genetic drift is a process, which mainly occurs in large populations. In
these, all alleles disappear by chance. ( )
b. Natural selection is the process that occurs when individuals with certain
characteristics possess a higher rate of reproduction than others, and it
works with genetic drift to ensure evolution. ( )
c. Genetic drifts occurred when there are changes in alleles. These will cause
eventualities like: mutations, and genetic recombination. ( )
5. Complete the following paragraphs to determine if they are founder effect or
bottleneck effect cases:
a. Hunting, habitat destruction, and intrusion of other animals have caused a
decrease in the population of Galapagos Turtles, with the resulting reduction
of their genetic diversity. This is an example of
___________________.
b. The population of Sardinia, Italy, was born from the migration of individuals
from Europe. After many generations, a study demonstrated that individuals
presented a high rate of cholesterol, situation of genetic origin. This is an
example of ___________________.
GLOSSARY
Load capacity: represented by the letter K, is the maximum number of individuals
of a specific population that a concrete ecosystem can maintain.
Diploids: a cell, an organism, or tissue that contains a double count of
chromosomes, meaning, two sets of chromosomes.
Elytra: the hard-shell wings of insects such as coleopterous and heteropterous.
Evolution: process by which organisms of a population change with time. Involves
changes in the frequency of hereditary features. In a synthetic manner, evolution is
the change in genetic frequency of a population.
Genotype: Genetic information of a particular organism, in the form of
deoxyribonucleic acid, DNA. Generally, the genome of a species has numerous
variations in its genes.
REFERENCES

Curtis, B., Barnes, S., Schnek, M. & Massarini, A. (2007). Biología (7a ed.).
Editorial Panamericana.

El Mundo. (2010). La fauna llegó a Madagascar en balsas naturales.
Recuperado de
http://www.elmundo.es/elmundo/2010/01/20/ciencia/1264011877.html

Escobar, R., Escobar, F., Gallego, G., Cortes, D., Chávez, A., Bohorquez,
A., Caicedo, A.L., Soto, M., Narváez, A., Lozano, E., Lugo, J. & Thhme, J. (2004).
La biotecnología en el salón de clases: documento de trabajo para docentes de
secundaria. Versión 1 (CD-ROM). Centro Internacional de Agricultura Tropical
(CIAT), Cali, Colombia.

FCV, UNNE. (2011). Revisión genética. Introducción a la Producción
animal. Recuperado de https://ipafcv.files.wordpress.com/2011/05/revision-paramejoramiento-genetico.pdf

Leaño, A. (2015). Monos araña albinos, señal de alarma. Recuperado de
http://www.uniandes.edu.co/noticias/ciencias/monos-arana-albinos-senal-dealarma

Molles, M. Jr. (2006). Ecología conceptos y aplicaciones (3ª ed.). Madrid:
McGraw-Hill-Interamericana.

Marín (2009). Arqueozoología en el cantábrico oriental durante la transición
Pleistoceno/Holoceno. Cantabria: Publican Ediciones.

Ovoa, M. & Usaquén, W. (2006). Diversidad genética de la población
colombiana de ganado cebú Brahman americano bos indicus (Bovidae). Acta
Biológica
Colombiana,
(11).
Recuperado
de
http://www.revistas.unal.edu.co/index.php/actabiol/article/view/27635

Oota, H., Pakendorf, B., Weiss, G., Von Haesele, A., Pookajorn, S.,
Settheetham-Ishida, W., Tiwawech, D., Ishida, T. & Stoneking, M. (2005). Recent
Origin and Cultural Reversion of a Hunter–Gatherer Group. PLOS Biology, 3 (3).
Recuperado de
http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.0030071

Patil, C. & Biradar, P. (2011). Molecular Biology. APH Publishing
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