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
http://www.rothamsted.ac.uk/notebook/courses/guide/dnast.htm

Figure 1. This diagram demonstrates the basic structure of DNA. (from http://www.accessexcellence.org/RC/VL/GG/dna_molecule.html)

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 http://www.bbc.co.uk/schools/gcsebitesize/biology/ variationandinheritance/0dnaandgenesrev4.shtml)

To learn more about the relationship between DNA, genes, and chromosomes see http://www.ncc.gmu.edu/dna/dna.htm

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. (from http://www.ornl.gov/sci/techresources/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 http://www.lbl.gov/Science-Articles/Archive/LSD-molecular-DNA.html

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.

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: http://www.accessexcellence.org/RC/VL/GG/comparison.html)

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 http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/main.html and http://www.biology.arizona.edu/cell_bio/tutorials/meiosis/main.html .

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 http://www.stanford.edu/group/stanfordbirds/text/essays/Birds,_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 http://books.nap.edu/html/creationism/evidence.html. 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 http://molvis.sdsc.edu/dna/index.htm

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 http://www.lewport.wnyric.org/JWANAMAKER/
animations/Protein%20Synthesis%20-%20long.html .

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 http://www.makingthemodernworld.org/learning_modules/biology/01.TU.03/?section=7

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
http://www.pbs.org/wgbh/evolution/library/01/4/l_014_01.html

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Performance Benchmark L.12.D.2

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

Sample Test Questions

1. Which of the following is true about the chromosomes found in the cells of every organism?
a. Daughter cells have half the number of chromosomes as parent cells.
b. All cells have at least eight chromosomes per cell.
c. The cells of a particular species have a distinctive number of chromosomes in their nuclei.
d. Chromosomes contain ribonucleic acid (RNA)

2. Great similarity in the DNA between species implies
a. recent common ancestry.
b. remote common ancestry.
c. successful reproduction.
d. successful mating between species.

3. The similarities of chimpanzee and human DNA indicates that the two species are most likely
a. identical
b. related through a recent ancestor
c. not related
d. evolving at a rapid rate

4. Observe the following base sequences of a portion of one strand of DNA from 4 different organisms

Based on this DNA evidence, which two organisms show the most recent common ancestor?
a. Organism A and B
b. Organism A and C
c. Organism B and D
d. Organism B and C

5. DNA sequences provide evidence of evolutionary relationships between organisms. Which of the following statements best supports this evidence?
a. DNA is only passed from the mother to the female offspring, who in turn make children to continue the family traits.
b. DNA can be found in the nucleus of every cell.
c. DNA never changes or decomposes over time;
d. DNA is passed from a parent cell to its offspring through meiosis and mitosis.

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

1. (c)
2. (a)
3. (b)
4. (a)
5. (c)

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Performance 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 http://learn.genetics.utah.edu/units/basics/tour/

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 http://www.indiana.edu/~ensiweb/lessons/chromcom.html

Another activity at the site allows students to investigate the relationship between molecular biology and phylogeny and can be found at http://www.indiana.edu/~ensiweb/lessons/mol.bio.html

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 http://www.indiana.edu/~ensiweb/lessons/p.tut.db.html

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 http://www.becominghuman.org/learning_cntr

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 http://www.ucmp.berkeley.edu/fosrec/Filson.html#TAB2

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 http://bioweb.uwlax.edu/GenWeb/Evol_Pop/Phylogenetics/Exercise/exercise.htm

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