Download Mutations WS

Increasing Genetic Diversity through DNA Mutations
Learning Objections:



SWBAT define DNA mutations and explain how they can influence the structure of a protein.
SWBAT describe and give examples of neutral mutations, harmful mutations, and beneficial
mutations.
SWBAT use the relationship between sickle-cell disease and malaria to describe how mutations
can increase genetic diversity of a group of organisms which can be important for the long-term
survival of the population.
INTRO VIDEO:
 http://learn.genetics.utah.edu/content/variation/sources/
Part I: TYPES OF MUTATIONS
Mutations are changes in the DNA. Mutations occur frequently, but these changes may or may
not impact the protein that the DNA codes for. Therefore, mutations may have negative
consequences, positive consequences, or may be neutral (inconsequential/no effect). In
the table below,
 Use the single stranded segment of DNA which is 9 bases long.
 Next, show the mRNA that the DNA segment will code for
 Finally show the 3 amino acids that will result from the 9 bases (3 codons).
Original (Unmutated) DNA, mRNA and amino acids:
Single Stranded DNA (9 bases) 
T T T G C A C C T
Corresponding mRNA (9 bases/ 3 codons) 
Amino Acid Sequence (3) 
1. Neutral Mutations: mutations that have no effect on the protein.
Example: In the table below,
 Use the DNA segment below. Note there is a single-base substitution to the original
DNA that will have NO effect on the amino acid sequence.
 Show the mRNA and the amino acid chain that will be formed from the mutated (changed)
DNA.
 Circle (or highlight) the mutation in the DNA and the resulting effect in mRNA.
Single Base Mutation with Neutral Effect
Single Stranded DNA (9 bases) 
T T C G C A C C T
Corresponding mRNA (9 bases/ 3 codons) 
Amino Acid Sequence (3) 
Since this single-base mutation does not change the structure of the protein, it also has no effect on
the function of the protein - therefore it is a neutral mutation.
2. Mutations with a consequence: Next, imagine a single-base substitution that DOES
impact the protein by changing only ONE amino acid. In some cases, this could be deadly (as
with Tay Sachs), but in other cases this could have very minor consequences that may be
harmful but not deadly (Sickle-Cell), or it could even result in a beneficial consequence (the
protein is better able to do its job, or gains a new function).
Single base substitution that alters a single amino acid:
Single Stranded DNA (9 bases) 
C T T G C A C C T
Corresponding mRNA (9 bases/ 3 codons) 
Amino Acid Sequence (3) 
Sometimes however, mutations can have very dramatic effects on the proteins produced. A
frameshift mutation results from the insertion or deletion of 1 or more bases.
Show the effects on the mRNA and on the amino acid sequence that result from the mutated
DNA segment in the example below. Circle the mutation in the DNA and mRNA.
Single Stranded DNA (9 bases) 
T T TG T T T C AC C T
Corresponding mRNA (9 bases/ 3 codons) 
Amino Acid Sequence (3) 
Compare this strand to the original unmutated DNA strand on page 1. Describe what type of
mutation has occured (insertion or deletion)…
This is an example of a Frameshift mutation as a result of a ___ base ___________.
PART II: MUTATIONS PRACTICE
1. During DNA replication, the following ORIGINAL strand of DNA is copied: A T A G C G C C C A T T
a) Create the complementary strand of DNA. This will be your ‘unmutated’ DNA strand
…A T A G C G C C C A T T
______________________________ - use this ‘unmutated’ strand as the template for part b
b) Transcribe and translate the ‘unmutated’ strand of DNA.
______________________________________________ - mRNA
______________________________________________ - amino acid chain
During DNA replication is when DNA mutations generally occur. Imagine the following complementary
strand is formed during DNA replication of the ORIGINAL strand of DNA.
Original strand…
…A T A G CG C C C A T T…
Complementary strand
…T T T C G C G G G T A A … -this is the ‘mutated’ strand
c) Where, in the complimentary strand, did a mutation occur?
d) What type of mutation occurred (Substitution or Frameshift)?
e) Transcribe and translate the mutated strand of DNA into a protein fragment (amino acid chain).
NOTE: Do not wait for a start codon – assume this is the middle of the protein, somewhere after the
‘start’
_____________________________________________________________________________ - mRNA
_____________________________________________________________________________ - amino acid chain
f) Compare and contrast the protein fragments formed in (b) and (e).
2. Now imagine this mutation.
Original strand:
…A T A G C G C C C A T T …
Complementary strand (copy):
…T A T C G C G G C T A A…
a) Where did the mutation occur?
b) What type of mutation occurred?
c) Transcribe & translate the mutated strand of DNA into a protein fragment.
___________________________________________________________________________________ - mRNA
___________________________________________________________________________________ - amino acid chain
d) Compare the protein fragments formed in (1b) and (2c). Why is this mutation considered ‘neutral’?
3. Now imagine this mutation!
Original strand…
… A T A G C G C C C A T T…
Complementary strand (copy):
… T A C G C G G G T A A C…
a) Where did the mutation occur?
b) What type of mutation occurred?
c) Transcribe & translate the mutated strand of DNA into a protein fragment.
_________________________________________________ - mRNA
_________________________________________________ - amino acid chain
d) Compare the protein fragments formed in (1b) and (3c).
e) Explain why frame shift mutations typically have more significant consequences than substitution
mutations.
4. Application: Think about the primary, secondary & tertiary structure of proteins. How can changing
the order and/or number of amino acids (via a mutation) ultimately alter the structure AND function of a
protein. Hint: recall what happened to your protein when you changed the amino acids (thumbtacks) in
the toober protein lab!!!!
PART III: CAUSES of MUTATIONS and their IMPACTS ON POPULATIONS
Anything that might cause a mutation is called a mutagen. A few examples include UV light,
ionizing rays, x-rays, and some chemicals (such as those present in tobacco smoke.)
Mutations can occur to either somatic (body) cells or to gametes (sex cells).
 If a mutation occurs in a somatic cell, it is NOT passed onto the next generation. However the
mutation is passed on to all new cells originating from the mutated cell. Many cancers are
caused from mutations to somatic cells – especially their proto-oncogenes and/or tumor
suppressor genes. When this mutated cell divides, the newly created cell also carries the
mutation, and so forth.
 If a mutation occurs in a gamete cell it CAN be passed on to the next generation. If the new
organism (formed from this gamete) survives and reproduces, the mutation will also be passed
on to all its descendants!
Summarize why only mutations to gametes are inherited/ passed on. ___________________
____________________________________________________________________
____________________________________________________________________
______________________________________________________________
______________________________________________________________
A) Harmful Mutations: Mutations that affect a key protein so dramatically that the protein
can no longer perform its critical function.
Example: Tay Sachs (a single base substitution) and Cystic Fibrosis (3 base deletion). Many
genetic diseases such as these are the consequences of heritable DNA mutations that have been
passed down from one generation to the next. Also, you can accumulate harmful mutations to your
DNA throughout your lifetime; accumulations of these mutations may result in cancer, or in other
cases may simply be part of the aging process.
B) Beneficial Mutations:
Mutation that enhance a protein’s ability to perform a function, or a mutation that produces a
protein that perform a new function are beneficial mutations.
Example: Lactose tolerance is a characteristic that gives humans with the ‘mutation’ the ability to
produce an enzyme that breaks down sugars in milk (lactose). Lactose tolerance is thought to have
arisen from a mutation in humans which provided an ‘advantage’ to those people who kept animals
and drank the milk. This mutation helped those people survive better in their environment and/or
reproduce more and therefore is considered beneficial.
Some of the most compelling examples of beneficial mutations in humans are those that correlate
with resistance to certain infectious diseases. As early as the 1950s researchers noted that the
sickle-cell mutation in the beta hemoglobin gene provided carriers of the trait with protection
against malaria (a major disease of tropical areas.) Since then, scientists have identified a number
of genetic variants that give some defense against other diseases (such as HIV and TB).
Sickle-Cell Anemia and Malaria Video Clip
https://www.youtube.com/watch?v=1fN7rOwDyMQ
http://www.pbs.org/wgbh/evolution/library/01/2/l_012_02.html (5 minutes)
ANSWER BEFORE VIEWING THE CLIP
1. Describe sickle-cell disease. HINT: you have studied this in multiple other assignments—
please refer to those assignments in your journal when completing the following...
The genetic cause of sickle-cell disease is a _______________________ resulting in a
misshapen ____________________ protein in red blood cells that carry ____________
throughout the body. The misshapen protein causes red blood cells to form _______________
shapes rather than round doughnut shaped cells and this prevents their free flow through
____________________________________. As a consequence, victims of sickle-cell
disease experience the following symptoms: _____________________________________
___________________________________________________________________.
ANSWER WHILE VIEWING or AFTER VIEWING CLIP
2. Complete the chart below regarding sickle-cell disease/sickle-cell trait.
Genotype
Phenotype
Resistant to Malaria?
3. Calculate: (a) What are the chances that heterozygous parents will have a child that has sicklecell disease? (b) What are their chances that a child will be homozygous for normal
hemoglobin? (c) What are the chances that a child will also be heterozygous? Show work using
a punnett-square.
4. Describe the malaria disease:
Malaria is caused by ___________________________________. Malaria is carried by
___________________________________ and is mainly found in ________________
______________________________ (where in the world). The symptoms of malaria are
___________________________________________________________________.
5. Explain why having an allele for the sickle-cell trait is an advantage in malaria ridden
countries.
6. Explain why genetic diversity is important for the long-term survival of human populations.
Use the variation in hemoglobin as an example (what might have happened to the human
population in malaria-ridden countries if all people had only normal hemoglobin).
Scientist Profile- Pardis Sabeti
http://www.pbs.org/wgbh/nova/sciencenow/0302/04.html (9 minutes)
Based on the video clip, complete each of the following prompts using at least 3 sentences each.
1. According to the clip beneficial mutations are. . .
2. Pardis Sabeti is…(describe who she is, her life, and what she does).