Download DNA, Genes, and Chromosomes

Reproduction, Life Cycles, and Heredity
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DNA, Genes, and
Chromosomes
Four friends were talking about human DNA, genes, and chromosomes. They each
had different ideas about where these structures were found. This is what they said.
Bella:
“I think DNA is found on genes.”
Kyra:
“I think chromosomes are found on genes.”
Kurt:
“I think genes are found on DNA.”
Joan:
“I think chromosomes are found on DNA.”
Whom do you agree with the most? __________ Explain why you agree.
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Uncovering Student Ideas in Life Science
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Reproduction, Life Cycles, and Heredity
DNA, Genes, and
Chromosomes
Teacher Notes
Purpose
The purpose of this assessment probe is to elicit
students’ ideas about structures they encounter when they learn about heredity. The probe
is designed to reveal students’ ideas about the
“parts and wholes” relationship between DNA,
genes, and chromosomes.
Related Concepts
DNA, genes, chromosome
Explanation
The best answer is Kurt’s: “I think genes are
found on DNA.” Genes are the basic structural
and functional unit of heredity. They are found
on chromosomes, which are made up of DNA,
histones, and other support proteins; therefore,
genes are found on DNA. A gene is a segment of
DNA that has a specific location on a chromosome. Humans have 23 pairs of chromosomes.
Our chromosomes come in pairs (except for the
X and Y chromosome in men), and each pair is
made up of a single molecule of double-stranded
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DNA tightly coiled many times around a protein called a histone that supports its structure. If
you imagine this strand of DNA being uncoiled
and stretched out, it might look like a long ladder. Each of the rungs of the ladder is called a
base pair, and segments of these base pairs of
varying lengths are called genes. Each gene
contains a piece of genetic information that tells
the cell to make a specific protein. Thousands
of genes are found on each strand of DNA that
makes up your chromosomes.
It had been thought that much of the length
of DNA does not seem to code for any specific
protein and does not seem to be genes. This
was long referred to as “junk DNA” and is now
more often referred to as noncoding and structural DNA. Current evidence indicates that
these regions are important for regulating gene
activity. They also help position DNA in threedimensional space within the nucleus, which in
turn affects rates of gene expression. Put another
way, DNA has information stored in its folding
patterns, not just in the GATC code.
N a t i o n a l S c i e n c e Te a c h e r s A s s o c i a t i o n
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Reproduction, Life Cycles, and Heredity
Curricular and Instructional
Considerations
Elementary Students
At the elementary level, students develop basic
ideas about heredity. The mechanism, cells,
and molecular structures involved in inheriting genetic traits are not addressed until middle and high school.
Middle School Students
Middle school students begin to develop the
genetic explanation for how traits are passed
on from one generation to the next. They combine their basic understanding of genetics with
their basic knowledge of cell structure, recognizing that chromosomes are found in the
nucleus and genes are found on chromosomes.
They learn that DNA is responsible for our
inherited traits passed on by genes, but details
about DNA should wait until students have a
deeper understanding of molecules.
High School Students
In high school, students develop a deeper
understanding of the structures involved in
genetics at a molecular level and understand
that genes code for specific proteins. They
should be able to distinguish between DNA,
chromosomes, and genes and know their relationship to one another. A growing understanding of biochemistry enables students to
learn about the structure of the DNA molecule
and how it functions in passing on inheritable
traits. They learn about the pioneering studies
of DNA and the scientific advances that led to
the sequencing of the human genome.
Administering the Probe
This probe is best used at the middle and high
school level with students who have some familiarity with these genetics concepts. At the high
school level, it can be used to elicit students’
preconceptions about the relationship among
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DNA, genes, and chromosomes. It can also
be used to monitor students’ understanding of
the relationship among these three structures
before proceeding with more advanced topics. Make sure students know that the DNA
referred to in the answer choices is the complete strand of DNA, not a segment of DNA.
Related Ideas in National
Science Education Standards
(NRC 1996)
K–4 Life Cycles of Organisms
• Many characteristics of an organism are
inherited from the parents of the organism, but other characteristics result from
an individual’s interaction with the
environment.
5–8 Reproduction and Heredity
Hereditary information is contained in
genes, located in the chromosomes of
each cell. Each gene carries a single unit
of information. An inherited trait of an
individual can be determined by one or by
many genes, and a single gene can influence
more than one trait. A human cell contains
many thousands of different genes.
9–12 The Molecular Basis of Heredity
In all organisms, the instructions for
specifying the characteristics of the organism are carried in DNA, a large polymer
formed from subunits of four kinds (A, G,
C, and T). The chemical and structural
properties of DNA explain how the genetic
information that underlies heredity is both
encoded in genes (as a string of molecular
“letters”) and replicated (by a templating
mechanism). Each DNA molecule in a cell
forms a single chromosome.
Indicates a strong match between the ideas elicited by the probe and a national standard’s learning goal.
Uncovering Student Ideas in Life Science
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Reproduction, Life Cycles, and Heredity
Related Ideas in Benchmarks
for Science Literacy
(AAAS 2009)
3–5 Heredity
• For offspring to resemble their parents,
there must be a reliable way to transfer
information from one generation to the
next.
6–8 Heredity
• In organisms that have two sexes, typically
half of the genes come from each parent.
• The same genetic information is copied in
each cell of the new organism.
9–12 Heredity
Genes are segments of DNA molecules.
Inserting, deleting, or substituting segments of DNA molecules can alter genes.
An altered gene may be passed on to every
cell that develops from it. The resulting
features may help, harm, or have little or
no effect on the offspring’s success in its
environment.
Related Research
•
•
•
In his research on common misconceptions related to heredity, Berthelsen (1999)
found that many students do not understand the relationship among DNA, genes,
and chromosomes.
Initial field test results of this probe show
that some middle and high school students
believe there is a hierarchical organization
inside the nucleus in which the chromosome is the structural unit that contains
genes and DNA molecules are found
within these genes.
A study of 16-year-old students in England
and Wales showed a poor understanding of
the processes by which genetic information
is transferred and a lack of basic knowledge about the structures involved. There
appeared to be widespread uncertainty and
confusion over the use of genetics concepts
such as genes and chromosomes (Lewis
and Wood-Robinson 2000).
Suggestions for Instruction and
Assessment
•
•
•
Ask students what they would see if they
had the magnification to see the details
inside the nucleus of a cell. Ask them to
keep zooming deeper from chromosome
to DNA to the segments of DNA (genes)
to the chemical bases that make up the
genes.
Take students on a “tour” of a chromosome. The Genetics Learning Center at the
University of Utah has a nice example of
an online tour at http://learn.genetics.utah.
edu/content/begin/traits/tour_chromosome.
html.
Listen carefully when students choose
“genes are found on DNA” as the answer
in the probe. These students may not realize genes are segments with a specific location on a DNA molecule. They may think
genes are just structures peppered throughout a DNA molecule. These students may
also confuse each of the bases that make
up a DNA molecule with being a gene.
Related NSTA Science Store
Publications, NSTA Journal
Articles, NSTA SciGuides,
NSTA SciPacks, and NSTA
Science Objects
American Association for the Advancement of Science (AAAS). 2001. Atlas of science literacy. Vol.
1. (See “DNA and Inherited Characteristics”
map, pp. 68–69.) Washington, DC: AAAS.
Koba, S., with A. Tweed. 2009. Hard-to-teach biology concepts: A framework to deepen student
understanding. Arlington, VA: NSTA Press.
Science Object: Cell Structure and Function: The
Molecular Machinery of Life.
Indicates a strong match between the ideas elicited by the probe and a national standard’s learning goal.
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N a t i o n a l S c i e n c e Te a c h e r s A s s o c i a t i o n
Copyright © 2011 NSTA. All rights reserved. For more information, go to www.nsta.org/permissions.
Reproduction, Life Cycles, and Heredity
Related Curriculum Topic Study
Guides (in Keeley 2005)
“DNA”
“Mechanism of Inheritance (Genetics)”
References
American Association for the Advancement of Science (AAAS). 2009. Benchmarks for science literacy online. www.project2061.org/publications/
bsl/online
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Berthelsen, B. 1999. Students’ naïve conceptions in
life science. MSTA Journal 44 (1): 13–19.
Keeley, P. 2005. Science curriculum topic study:
Bridging the gap between standards and practice.
Thousand Oaks, CA: Corwin Press and Arlington, VA: NSTA Press.
Lewis, J., and V. Wood-Robinson. 2000. Genes,
chromosomes, cell division, and inheritance:
Do students see any relationship? International
Journal of Science Education 22 (2): 177–195.
National Research Council (NRC). 1996. National
science education standards. Washington, DC:
National Academies Press.
Uncovering Student Ideas in Life Science
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