| Students
know several causes and effects of somatic versus sex cell mutations.
E/S
Mutations are simply changes in the DNA code. The first thing that
a student should understand when studying mutations is the difference
between a somatic cell and a sex cell. A somatic cell is a body cell
that has a full complement of chromosomes while a sex cell (or germline
cell) is a cell involved in sexual reproduction with half the number
of chromosomes. Therefore, mutations can be separated into germline
mutations, which can be passed on to offspring, or somatic mutations,
which only affect the individual.
Gene Level Mutations
1. Point Mutation (or substitution)
This type of mutation is where only a single nucleotide in a gene
has been changed. The effect can be quite dramatic. The result can
be a nonsense triplet which will stop the protein’s construction.
This will result in truncated proteins. A missense triplet may result
coding for a different amino acid resulting in an incorrect protein.
Lastly, silent mutations may occur coding for the same amino acid
which results in no change to the protein.
Point mutations hay happen spontaneously when mistakes are made during
DNA replication. The incidence of mutations can be increased by mutagens.
A mutagen is a physical or chemical agent that can be harmful to DNA.
Examples of mutagens are radiation (UV rays) or chemical (carcinogens).
Sickle Cell Anemia is an example of a point mutation. It is the most
common inherited blood disorder affecting 72,000 Americans (www.ncbi.nlm.nih.gov).
It is caused by the point mutation of a single amino acid, resulting
in a valine being substituted for glutamine.
2. Frameshift Mutations
A frameshift mutation results in the addition or deletion of nucleotides
in the DNA sequence. Three nucleotides (a triplet) are translated
into an amino acid through the process of translation. The addition
or subtraction of nucleotides will shift the entire
Chromosomal Level Mutations
Chromosomal mutations take place during cell division, either mitosis
or meiosis. During cell division, the chromatin material shortens
and thickens into chromosomes. A chromosome consists of two duplicate
sister chromatids connected by a centromere. Each chromatid should
separate and travel to opposite ends of the cell to create two identical
daughter cells. Sometimes, mistakes happen in the separation of sister
chromatids.
1. Reciprocal Translocation
Translocation is the transfer of a part of a chromosome with another
nonhomologous chromosome during cell division. Chromosomes are actually
fairly fragile and some break during cell division and the broken
bits rejoin with neighboring chromosomes. If there is no loss of genetic
information, the translocation is usually harmless. However, it can
have reproductive results. A person who is a “carrier”
of a translocation may have a higher incidence of miscarriage or have
a higher probability of having a child with birth defects.
2. Chromosomal Deletion/Duplication
A chromosomal deletion is just what it sounds like. A segment of DNA
is lost in the cell during cell division. The lost piece broke off
a chromosome and attached to the homologous chromosome. The result
in cell division is one daughter cell has duplicate DNA and the other
daughter cell is missing the same DNA sequence. The result can be
detrimental. It can result in an unbalanced number of chromosomes.
The resulting karyotype may be 45 or 47 (instead of 46) resulting
a variety of birth defects. In somatic cells, an addition/deletion
may also result in various types of cancers, especially leukemia.
3. Inversion mutation
In inversion mutation is where a piece of a chromosome breaks off
and is reattached in reverse order. Inversions don’t appear
to be harmful in the individual as long as there is no loss or gain
of DNA. However, they are now a carrier and a resulting offspring
has a small chance of inheriting an unbalanced chromosome arrangement
with missing or extra components. (See Figure 6)
4. Nondisjunction/Polyploidy
The addition or loss of an entire chromosome is called nondisjunction.
It results when two chromosomes remain connected instead of separating
during meiosis. The result is extra or missing chromosomes. For example,
an individual that inherits three copies of chromosome 21 (47 chromosomes)
has a condition called Down’s syndrome. Most cases of nondisjunction
results in nonviability of an offspring. Nondisjunction can also result
in the development of cancers.
If an entire set of chromosomes fail to separate, a condition of
polyploidy results. This is commonly found in plant cells.
Somatic mutation vs. Gamete mutation
A somatic mutation is a mutation that takes place in any single cell
of an organism except gametes and is not inheritable. Some current
studies have suggested that a lifetime of accumulated mutations is
why we age. Another result of harmful somatic mutations is cancer.
The mutation starts in a single cell and as this cell divides uncontrollably,
a tumor develops.
A mutation in sex cells results in an inheritable mutation. This
mutation starts in a gamete (ie. egg, sperm, pollen, or ovule) and
is passed into the resulting offspring. This genetic change, is therefore,
present in every cell of the organism. Some genetic defects cannot
result in a viable offspring. But if it does, a variety of genetic
disorders can be expressed.
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Content
Benchmark L.12.A.4
Students know several causes and effects of somatic versus sex cell
mutations. E/S
Common misconceptions associated with this benchmark:
1. Students often have difficulty conceptualizing gene
expression (via protein synthesis) and that changes in the DNA code
can be reflected in changes in gene expression.
Students have trouble seeing the big picture and following the pathway
of DNA relationship through to gene expression. It is a very abstract
complicated process that involves many steps and it’s easy for
students to get lost in the details, so they give up. It is important
that teachers break down each step and convey its relevance before
moving onto the next step. Students need to have a good foundation
in transcription, translations, and replication before mutations are
introduced. Otherwise, the idea of mutations would only compound their
confusion.
2. Students may understand how DNA is replicated, transcribed,
and translated, but they still may not understand how a gene controls
a trait.
Again, students have trouble seeing how one process plays into another.
They may be able to draw the diagrams and flow charts but when asked
to describe the purpose of each step students are often stumped. “So
you may need to explain "up" or "down" how the
parts relate to the whole -- up, how the item under discussion fits
into something bigger, and down, how the item is made of smaller things.
For example, if you are discussing genes, you should be prepared to
go "up" to chromosomes, genomes, traits, etc., and "down"
to DNA, codons, nucleotides, and bases.”
For more information about this misconception please visit this site:
http://cirtl.wceruw.org/diversityresources/resources/resource-
book/overcomingmisconceptions.htm
3. Students think that all mutations are inheritable
and have trouble differentiating between somatic and germline mutations.
Students can tell you that all life forms are made up of cells and
can even describe mitosis, but when pressed some still have misconceptions
about how we start as a single cell. This single cell divides into
two, then four, then eight, etc. The resulting ball of cells all have
the identical set of instructions but begin to differentiate and take
on specific roles. Students have a hard time understanding that a
skin cell and a liver cell have the same identical set of instructions
but use only portions of the code specific to the cell’s job.
Students also misunderstand that cells continue to divide and grow
even as adults and that mutations can occur in an adult skin cell
that results in skin cancer. Students are also confused as to how
a genetic mutation is passed on to offspring (L12A5).
For more information concerning misconceptions about genetic mutations
please visit
(http://cirtl.wceruw.org/DiversityResources/resources/
resource-book/overcomingmisconceptions.htm)
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Content
Benchmark L.12.A.4
Students know several causes and effects of somatic versus sex cell mutations. E/S
Sample Test Questions
1st Item Specification: Describe the difference between sex cells and somatic cells in an organism.
Depth of Knowledge Level 1
- Which of the following is NOT a somatic cell?
- Cheek cell
- Sperm cell
- Blood cell
- Nerve cell
- Which of the following statement correctly describes a sex cell and somatic cell? A sex cell is
- haploid and a somatic cell is haploid.
- diploid and a somatic cell is diploid.
- diploid and a somatic cell is haploid.
- haploid and a somatic cell is diploid.
Depth of Knowledge Level 2
- Which process occurs in somatic cells?
- Use the following diagram to answer the following question.
Which of the above cell processes contribute to genetic diversity?
- 1 and 2
- 2 and 3
- 3 and 4
- 1 and 4
2nd Item Specification: Explain that mutations in sex cells may be passed on to offspring.
Depth of Knowledge Level 1
- Changes in the genetic material in sex cells are mutations that
- may be transmitted to the next generation.
- are always eliminated during meiosis.
- are always sex-linked.
- cannot affect the organism or its offspring.
- A mutation can be passed on to offspring if the mutation takes place in
- a liver cell.
- an egg cell.
- a uterus cell.
- a skin cell.
Depth of Knowledge Level 2
- Nondisjunction of sex chromosomes in a human female during meiosis may result in her son inheriting the disorder represented by
A. XXY
B. XYY
C. XXX
D. YYY
- A child born with Down Syndrome (Trisomy 21) can have parents without the disorder. Down Syndrome is caused by
- three point mutations in the 21st chromosome of an egg or sperm cell.
- the nondisjunction of chromosome 21 in a somatic cell.
- three point mutations in the 21st chromosome a somatic cell.
- the nondisjunction of chromosome 21 in an egg or sperm cell.
3rd Item Specification: Explain that mutations in somatic cells are not passed on to offspring.
Depth of Knowledge Level 1
- Nonlethal mutations in somatic cells
- are found in egg cells and are passed onto female offspring.
- are found in sperm cells and are passed onto male offspring.
- results in the death of the body cell with the mutation.
- are mutations in body cells and are not passed onto offspring.
- Genetic mutations that are not passed on to offspring are found in
- egg cells.
- sperm cells.
- somatic cells
- gamete cells.
Depth of Knowledge Level 2
- An adult develops melanoma which is a type of skin cancer. The cancer
- can be passed onto children because the cancer is in a gamete cell.
- can be passed onto children because the cancer is in a somatic cell.
- cannot be passed to any children because the cancer is in a gamete cell
- cannot be passed to any children because the cancer is in a somatic cell.
- Ionizing radiation can damage DNA molecules. If DNA damage occurs in blood tissue it
- can be inherited because the DNA mutation is in a gamete cell.
- can be inherited because the DNA mutation is in a somatic cell.
- cannot be inherited because the DNA mutation is in a somatic cell.
- cannot be inherited because the DNA mutation is in a gamete cell.
4th Item Specification: Explain that environmental factors may cause mutations in DNA in both somatic cells and sex cells.
Depth of Knowledge Level 1
- Environmental substances that can cause cancer are called
- tumors.
- carcinogens.
- mutations.
- poisons.
- Environmental factors like ultraviolet light, asbestos fibers, and cigarette smoke are
- harmless and do not cause lasting cellular damage.
- only temporarily damaging to cellular DNA.
- carcinogenic resulting in permanent DNA changes.
- damaging to only somatic cells and no effect on gametes.
Depth of Knowledge Level 2
- What is the BEST reason why many societies have banned or dramatically decreased the production of chemical such as formaldehyde and asbestos? The chemicals have been linked to
- increased cellular mutations.
- causing sterility in lab rats.
- heavy metal poisoning.
- uncontrolled meiotic divisions.
- The graph below shows the 15 most commonly reported environmental factors that may have caused cancer clusters. A cancer cluster is an area that has a significantly higher rate of cancer.
(From http://www.ehponline.org/members/2006/9021/9021.html)
Which type of environmental factor is most likely to cause a cancer cluster?
- Specific chemicals
- Chemical mixes
- General exposures
- Pollution sites
5th Item Specification: Recognize that mutations result from changes in DNA.
Depth of Knowledge Level 1
- The information below represents a change in a portion of the base sequence in a DNA molecule.
 
This change can best be interpreted as a(n)
- point mutation.
- Translocation mutation.
- frameshift mutation.
- inversion mutation.
- A gene mutation results from a change in the
- sequence of nucleotides in RNA.
- chromosome number in a gamete.
- sequence of the nucleotides in DNA.
- chromosome number in a somatic cell.
- A mutation is defined as
- a change in an organism’s DNA sequence.
- the growth of an abnormal tumor.
- the changing of a cell from one type to another.
- a way of changing mRNA to proteins.
Depth of Knowledge Level 2
- Which of the following sequences has a point mutation from TTAGCTACG?
- AAUCGAUGC
- TTAGCTACG
- TTACCTACG
- AATCGATGC
21. Use the table showing mRNA codons to answer the question below.
(From http://www.safarikscience.org/biologyhome/7_dna/codon_question.png)
The following mRNA sequence codes for the amino acids in a segment of the gene that codes for normal hemoglobin.
Normal Codons:
GUU – CAC – CUA – ACA – GAA – GAG – AAA
Mutated Sequence:
GUU – CAC – CUA – ACA – GAA – GAC – AAA
A mutation occurred in normal hemoglobin causing a disease called Sickle Cell Anemia. Which of the following sequences is the result of the mutation?
- Val – His – Leu – Ala – Pro - Glu – Glu – Lys
- Val – His – Leu – Thr – Pro – Glu - Asp – Lys
- Val – Ser – Leu – Thr – Pro – Glu – Glu - Lys
- Val – Ser – Leu – Thr – Pro – Gly – Glu – Lys
Content Benchmark L.12.A.4
Students know several causes and effects of somatic versus sex cell mutations. E/S
Sample Test Question Answers
- B, DOK Level 1
- D, DOK Level 1
- D, DOK Level 2
- B, DOK Level 2
- A, DOK Level 1
- B, DOK Level 1
- A, DOK Level 2
- D, DOK Level 2
- D, DOK Level 1
- C, DOK Level 1
- D, DOK Level 2
- C, DOK Level 2
- B, DOK Level 1
- C, DOK Level 1
- A, DOK Level 2
- A, DOK Level 2
- A, DOK Level 1
- C, DOK Level 1
- A, DOK Level 1
- C, DOK Level 2
- B, DOK Level 2
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Content Benchmark L.12.A.4 Students
know several causes and effects of somatic versus sex cell mutations.
E/S
Intervention Strategies and Resources
The following is a list of intervention strategies and resources
that will facilitate student understanding of this benchmark.
1. Animated sequences on the cause of cancer
This website has great animations that show students the cause of
cancer from a chromosome level down to the nucleotide level. It also
has information on different types of mutations with colorful, simple
diagrams. The website does go into a lot of detail about cancers but
the “Genetic Change” section is quite appropriate for
this benchmark and addresses some of misconceptions associated with
this benchmark.
To access the information and animated sequences visit:
http://www.cancerquest.org/index.cfm?page=53
2. Webquest activity on the use of technology
in diagnosing disease
This webquest illustrates the use of technology in diagnosing an unknown
disease. This activity is appropriate for higher level students. “It
will introduce students to the concepts of bioinformatics, genetic
diseases, and potential careers in science fields. This webquest activity
can be used in many different ways in your classroom. It is recommended
that students be divided up into groups of four, so that each student
can assume the role of one of the medical investigation team members.
This encourages cooperative learning in the student groups and also
gives students a chance to work as a team, much the way a real-world
investigative team might do. Alternatively, the webquest can be completed
by students individually, investigating all four roles by themselves.
Either way, emphasis should be made on having the students communicate
their findings by creating a presentation using multimedia whenever
possible. This webquest is designed to take approximately one week.
It would be possible to do a shortened webquest with only the bioinformatics
section, which should take one class period.”
To access the information visit:
http://www.koshland-science-museum.org/teachers/webquest.jsp
3. Extensive information about Genetics
“DNA from the Beginning is organized around key concepts. The
science behind each concept is explained by: animation, image gallery,
video interviews, problem/self quizzes, biographies, and links.”
This site has a wide range of topics grouped in three categories:
Classical Genetics, Molecules of Genetics, and Genetic Organization
and Control. A sampling of topics is below.
-Sex cells have one set of chromosomes; body cells have two
- All cells arise from pre-existing cells.
- Chromosomes carry genes.
- Genes get shuffled when chromosomes exchange pieces.
- One gene makes one protein.
- A gene is made of DNA.
- Mutations are changes in genetic information.
- Some types of mutations are automatically repaired.
- DNA is packaged in a chromosome.
- Different genes are active in different kinds of cells.
To access the information visit:
http://www.dnaftb.org/dnaftb/
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