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Content Benchmark L.12.D.2
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Students know similarity of DNA sequences gives evidence of relationships between organisms. E/S

When teaching all of the L.12.D benchmarks, it is imperative to help students understand the process of science. Most misconceptions about evolution are directly related to the misunderstanding of how science works. When students understand the nature of science, they will understand how scientists have studied the process of evolution. As questions arise about a “supernatural” creation of Earth and the Universe, students who understand the nature of science will understand why supernatural forces cannot be studied as part of scientific processes.

Cells of all organisms contain deoxyribonucleic acid, or DNA, which contains the information that determines, and controls cellular functions. The building blocks or monomers of DNA are called nucleotides. Each nucleotide consists of a phosphate group, a sugar (deoxyribose) and one of 4 nitrogenous bases. The nitrogenous bases are adenine, guanine, cytosine, and thymine. The nucleotides of DNA are often referred to by a letter, which represents the base: A, T, G, or C.

To learn more about the structure of DNA, see

(Click Image to Enlarge)
Figure 1. This diagram demonstrates the basic structure of DNA.

Particular segments of the DNA are called genes, and it is a gene that codes for the synthesis of a particular protein. Proteins determine the characteristics of a cell. The DNA nucleotide sequence and, more specifically the genes, give an organism its specific characteristics. For example, there are genes in human cells that code for the color of eyes, hair, and skin. There are also genes that code for the production of hormones, digestive enzymes, insulin, and all of the other proteins produced by cells. Large organized molecules of DNA in cells are called chromosomes. Chromosomes consist of the genes, regulatory and other intervening sequences of nucleotides, and proteins that help in the packaging of the DNA. Different organisms contain different types, sizes and number of chromosomes. Even though the chromosomes are different between organisms, the basic chemical structure of the DNA is the same in all organisms.

Figure 2. This diagram illustrates the relationship between DNA, genes, and chromosomes. (from

To learn more about the relationship between DNA, genes, and chromosomes see

Although organisms in different classification groups (genus, species, etc.) may be completely different, the fundamental chemical make-up of DNA is the same in all organisms. The building blocks, called nucleotides, that make up the DNA in all organisms are the same: A, T, G, and C. It is the sequence of these nucleotides, and ultimately the number, type, and sequence of genes that makes one organism different from another. The nucleotides that make up DNA can be compared to our alphabet. All words in our language and many other world languages are made up of groupings of the same 26 letters. DNA has only 4 “letters”, but because DNA is a very long molecule, the number of variations in DNA is enormous.

Figure 3. This figure illustrates a piece of DNA replicating.
Human_ Genome/publicat/primer/fig4.html

Before a cell divides, the DNA in the nucleus replicates itself. The mechanism for the replication process is controlled via the same processes in all three domains of life (Archaea, Bacteria, and Eukarya). It is not understood exactly how this replication process has remained in place for approximately 3.5 billion years during which life has existed on Earth.

For discussion of research that provides evidence of nucleus replication, see

Two general types of reproduction occur in organisms, both requiring cellular replication. In asexual reproduction, a cell will copy its DNA, then through complex processes called mitosis and cytokinesis, will split into two cells, each having a copy of the original cell’s DNA. In sexual reproduction, specialized sex cells will copy their DNA, then through complex process called meiosis and cytokinesis, will split into up to four cells, each containing half of the DNA of the original.

(Click Image to Enlarge)
Figure 4. This diagram illustrates what occurs with the DNA (chromosomes) during mitosis and meiosis. Note that before either division, the DNA in the cells replicate. (from:

Through many replications, changes in the DNA can occur. However these changes result only in different sequences of the nucleotides. The actual types of nucleotides do not change. As stated above, the DNA of all organisms is composed of the same chemical building blocks.

To learn more about mitosis and meiosis, see and .

With modern technology, scientists are able to determine the sequence of nucleotides in pieces of DNA. Using this technology, scientists have been able to study and compare DNA of many organisms and the similarity between DNA samples is used to determine relationships between organisms. Because biological evolution involves genetic changes (mutations) over time, the evolutionary relationship of organisms can be determined by comparing DNA. Different species with very similar DNA more recently descended from a common ancestor than did species with very different DNA. There is only about 0.1 percent difference in the DNA among different humans. The DNA of the species closest to humans, the chimpanzee is about 98 percent identical to that of humans.

To read about one example of how DNA and other scientific evidence has been used to determine the evolutionary relationship between different species of similar organisms (birds), see,_DNA.html

Because DNA codes for the production of proteins, comparison of proteins between species also provides evolutionary relationships between organisms. Cells of organisms that more recently shared a common ancestor will have a greater similarity in proteins produced than organisms that are more distantly related.

To read more about how molecular biology and DNA technology are used to determine relationships between organisms, see This article from the National Academies of Science discusses various scientific studies and disciplines that support the theory of biological evolution.

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Performance Benchmark L.12.D.2

Students know similarity of DNA sequences gives evidence of relationships between organisms. E/S

Common Misconceptions associated with this benchmark

1. Students do not understand that the chemical makeup of DNA is the same in all living organisms.

Molecules and basic life processes are common throughout all living organisms. If students successfully learn about basic biochemistry and cellular functions, it should be easy to help them understand the significance of DNA in identification and interrelationships of organisms. The chemical structure of DNA is the same in all organisms. Every molecule of DNA contains the same building blocks, or monomers, called nucleotides. The differences between organisms result from different numbers and orders of nucleotides. James Watson and Francis Crick were the first to describe the structure of DNA in 1953. Since then, the DNA of many organisms has been studied and the molecular basis for inheritance in all organisms has been confirmed.

To review the structure of DNA, see

2. Students do not understand how a genetic change (change in DNA) can result in a phenotypic change.

DNA provides the directions, or the blueprint for protein production in cells. The order of nucleotides in specific segments of DNA directs the production of proteins. As students learn about protein synthesis, they will learn how the information in DNA gets translated into a series of amino acids which then eventually becomes protein. When teaching genetic change, mutations, and evolution it may be necessary to review the process of protein synthesis, emphasizing what happens when a change or a mutation in the DNA occurs.

For a good, easy to understand review of protein synthesis, see

A common example of the effects of a mutation is the production of hemoglobin, an oxygen carrying protein found in blood. “Defective” hemoglobin is produced when a different nucleotide is substituted for one specific correct nucleotide in the DNA segment coding for hemoglobin production. This one tiny change results in the substitution of one amino acid in a long chain of amino acids. This change causes a phenotypic change: producing hemoglobin that is not as effective at transporting oxygen. Mutations in DNA can occur due to normal cellular processes, environmental conditions, errors during DNA replication, or randomly by chance.

Just as a mutation in the DNA coding for hemoglobin can cause a phenotypic change, a mutation in any piece of DNA that codes for a protein can result in a phenotypic change in the cell and that organism. Of significance to evolution is when a mutation occurs in a gamete (sex cell) because that mutation will affect traits in future generations.

For an easy to follow discussion of mutations and evolution, see

3. Students incorrectly think that if organisms look alike, then they must have common evolutionary decent.

When asked to classify organisms, students use obvious physical features, rather than processes or genetic relationships. Convergent evolution is the development of similar traits or characteristics by taxonomically different groups of organisms. Convergent evolution often occurs when two groups of organisms occupy similar niches. Just because two organisms may have developed a similar characteristic trait, it does not necessarily mean that they are closely related. For examples, birds and bats both have wings, an adaptation that allows them to fly. However, bats and birds evolved independently of each other.

For a discussion of convergent evolution, go to

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Content Benchmark L.12.D.2

Students know similarity of DNA sequences gives evidence of relationships between organisms. E/S

Sample Test Questions

1st Item Specification: Describe DNA as biochemical evidence for evolution.

Depth of Knowledge Level 1

  1. Which of the following is a form of biochemical evidence that can be used to study evolution?
    1. Homologous structures
    2. Intermediate forms
    3. Embryology
    4. Amino acid sequences
  1. Commonalities in DNA sequences of different species support the theory of
    1. heredity.
    2. evolution.
    3. artificial selection.
    4. gradualism.

Depth of Knowledge Level 2

  1. The fact that vital proteins such as cytochrome-c and DNA polymerase are found in almost every living thing indicates
    1. a common ancestor of all life in the very distant past.
    2. each species evolved separately through history.
    3. a common ancestor in some species, but not all species.
    4. the RNA sequences between species will be identical.
  1. Cytochrome-c is a protein found in many plants, animals, and unicellular organisms. The amino acid sequences may differ between different species, but the function and most of the sequences are the same. What could you infer based on this data?
    1. The protein is a random genetic defect in many species and indicates no common ancestry.
    2. The presence of this protein in many different species indicates common ancestry.
    3. The fact that the protein differs among different species indicates no common ancestry.
    4. Most proteins found in plants, animals, and unicellular organisms have similar amino acid sequences.

2nd Item Specification: Identify relationships between organisms based on similarities in DNA sequences.

Depth of Knowledge Level 1

  1. Closer similarities in the DNA sequences of two organisms of different species indicates
    1. A common ancestor between the two species.
    2. Homologous structures between the two species.
    3. Genetic defects between the two species.
    4. Artificial selection between the two species.
  1. The occurrence of the same blood protein in a group of species provides evidence that these species
    1. evolved in the same habitat.
    2. evolved in different habitats.
    3. descended from a common ancestor.
    4. descended from different ancestors.
  1. The table below shows a hemoglobin comparison between humans and several other organisms. Hemoglobin is a protein found in many animals.
Hemoglobin comparison
Animal with Hemoglobin Amino Acids that differ from human hemoglobin
gorilla 1
rhesus monkey 8
mouse 27
chicken 45
frog 67
lamprey 120

According to the table, which organism is most closely related to humans by ancestry?

  1. Lamprey
  2. Chicken
  3. Gorilla
  4. Monkey
  1. Cytochrome-c is a protein that is involved in cellular respiration in all eukaryotic organisms. Human cytochrome-c contains 104 amino acids. The following table compares human cytochrome-c with cytochrome-c from a number of other organisms.
Organism Number of cytochrome-c amino acidsthat differ from human cytochrome-c amino acids
Chickens 18
Chimpanzees 0
Dogs 13
Rattlesnakes 20
Rhesus monkeys 1
Yeasts 56

Which of the following is NOT a valid inference from these data?

  1. Dogs are more closely related to humans than rattlesnakes.
  2. Dogs are more closely related to humans than chickens.
  3. Chimpanzees and rhesus monkeys differ by one amino acid.
  4. All of the proteins produced by chimpanzees and humans are identical.
  1. A biologist analyzes the DNA sequences in three different animals. The biologist finds that animal 1 and 3 have nearly identical DNA sequences. The DNA sequences in animal 2 are significantly different from those of animal 1. From this information, the biologist may infer that
    1. animals 1 and 2 are more closely related to each other than either is to animal 3.
    2. animals 1 and 3 are more closely related to each other than either is to animal 2.
    3. all three animals appeared on Earth at about the same time and have a common ancestor.
    4. animal 3 must have been the distant common ancestor of both animal 1 and animal 2.
  1. The DNA sequence from an endangered pupfish was compared to the DNA samples collected from closely related fish species. The table below shows a portion of the DNA sequences from each of the fish species.
Pupfish DNA Sequence: ATT AAG CCG ATA

List the fish from the least to most closely related to the pupfish.

  1. Fish 1, Fish 2, Fish 3, Fish 4
  2. Fish 3, Fish 2, Fish 4, Fish 1
  3. Fish 3, Fish 4, Fish 1, Fish 2
  4. Fish 2, Fish 3, Fish 4, Fish 1

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Content Benchmark L.12.D.2

Students know similarity of DNA sequences gives evidence of relationships between organisms. E/S

Answers to Sample Test Questions

  1. D, DOK Level 1
  2. B, DOK Level 1
  3. A, DOK Level 2
  4. B, DOK Level 2
  5. A, DOK Level 1
  6. C, DOK Level 1
  7. C, DOK Level 1
  8. D, DOK Level 2
  9. B, DOK Level 2
  10. C, DOK Level 2

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Content Benchmark L.12.D.2

Students know similarity of DNA sequences gives evidence of relationships between organisms. E/S

Intervention Strategies and Resources
The following list of intervention strategies and resources will facilitate student understanding of this benchmark.

1. Tour of Basic DNA
This activity from the University of Utah provides students with a tour of basics of DNA. The “tour” can help the students understand the differences between DNA, genes, chromosomes, and proteins.

You can access this tour at

2. DNA and Biological Evolution Lessons
The Evolution and Nature of Science Institutes at the University of Indiana has created several lessons to teach about biological evolution.

One of the lessons shows chromosomal relationships between human and chimpanzees. The activity explores how chromosomal similarities suggest biological relationships.

To access this activity, go to

Another activity at the site allows students to investigate the relationship between molecular biology and phylogeny and can be found at

A third lesson investigates evolutionary questions using online molecular databases. This activity guides students through the use of online databases, and molecular information to answer questions about the biological relationships between several organisms and can be found at

3. Human Evolutionary Relationships
The Institute of Human Origins has created a Web site called Becoming Human. The site’s learning center has three biology lessons. Two of the lessons, Calculating Cousins and the Chromosome Connection relate directly to the information on the benchmark.

To access these lessons, go to

4. Online phylogeny activity to determine the relationship of a group of lizards
This activity from the UCMuseum of Paleontology allows students to practice phylogeny, using geographical, geological and physical attributes, then, finally using DNA evidence to deduce phylogeny of closely related lizards.

You can get the activity at

5. Online phylogeny activity using DNA evidence.
The BioWeb site is produced by faculty members at 14 difference University of Wisconsin campuses. The site contains BioLearn, as resource for high school students and teachers. One of the site’s activities allows students to create a phylogenic tree of several organisms based on DNA sequences.

To access the site, go to

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