Performance Benchmark L.12.D.2
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.blc.arizona.edu/Molecular_Graphics/DNA_Structure/DNA_Tutorial.HTML#Compo
nents
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/0dnaandgenesrev
4.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_Geno
me/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.
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://www.blc.arizona.edu/Molecular_Graphics/DNA_Structure/DNA_Tutorial.HTML#Compo
nents
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
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:
Organism A TTC CTA GGA TCC TTA GCA CAT TGC CCA TTT
Organism B TTC GTA GGA TGC TTA GCA CAT TGC CCA TTT
Organism C TTC CTA GGA TCC TTT CGT CAT TGC CCA TTT
Organism D TCC GGA GGA TGG TTA CCA CCT CCC GGG ATT
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.
Performance Benchmark L.12.D.2
Students know similarity of DNA sequences gives evidence of relationships between organisms.
E/S
Answers to Sample Questions
1.
2.
3.
4.
5.
(c)
(a)
(b)
(a)
(c)
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