Download Genes for Speed or Endurance?

Genes for Speed or Endurance?
Muscle power
Skeletal muscles are made of long cells
called muscle fibres. There are two types
of muscle fibres, slow twitch or muscle
contraction and fast twitch.
Fast twitch fibres fire more rapidly with
more force than slow twitch fibres.
Slow twitch fibres are more efficient in
using oxygen to generate energy, while
fast twitch fibres are less efficient in
energy generation.
Genetics
The DNA molecule is the carrier of genetic information.
Genes consist of the four types of DNA building bases
called A, C, G, & T. The order of these bases on the
chromosomes codes for assembling the order of amino
acids to make a protein. Proteins make cells.
Athletic performance is built upon good genetics,
nutrition, training and mental traits.
DNA testing can now be used to profile genetic
variations that are associated with power or endurance.
The identification of suitability genes in young athletes
might enable better decision-making about which sport
their physiology equips them for.
The relative
contributions of training and genetics to success seem to
vary depending on the sport and the person but some
companies are now offering the tests.
ACTN3 in muscle fibre
Mutation in ACTN3 gene
The major protein components of skeletal muscle
are actin and myosin.
Actin filaments are stabilized by actin binding
proteins or actinins of which there are two types, 2
and 3. Specific genes, ACTN2 and ACTN3, code for
these actinin proteins respectively. ACTN3 is
expressed only in fast twitch fibers
A mutant form of the ACTN3 gene has a single base
substitution in the DNA and is referred to as R577X or X.
This mutation (R577X) inserts a premature stop codon
into the gene for actinin 3 and does not produce the
protein. People with this gene do not produce actinin 3
in their fast twitch fibers.
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What does this DNA mutation mean?
No disease is associated with this genetic mutation. Around 16% of the world population is predicted to have
the congenital deficiency of actinin-3. Scientists think variations in this gene evolved in response to energy
needs of people in different parts of the world during human evolution.
Studies have linked the fiber twitch type (fast / slow) with ACTN3, i.e. fast twitch fiber abundant individuals
carry the normal version R of ACTN3 and this version is associated with sprint performance while the mutant
or non-functional version X is associated with endurance. As people have two copies of each gene they can be
RR, RX or XX for the ACTN3 gene.
Research has suggested an association between an individual's ACTN3 genotype and athletic performance:
R/R genotype: power advantage
X/X genotype: endurance advantage
R/X genotype: contributes to both power and endurance
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Testing for ACTN3
The scenario: To test seven young
athletes for their ACTN3 genes
Your task:
To use PCR to identify the ACTN3
genotype of the seven DNA samples.
Method: PCR reaction (done before the lab) PCR is used to copy small pieces of DNA in the test-tube.
1. Components were added as in the table below and put into PCR machine for 30 cycles.
Tube 1 Tube Tube
Tube Tube Tube Tube Tube
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Mastermix (contains primers,
13µL
13µL 13µL
13µL 13µL 13µL 13µL 13µL
dNTPS, MgCL 2 , buffer)
1. Control R/X
1µL
2. Test A DNA
1µL
3. Test B DNA
1µL
4. Test C DNA
1µL
5. Test D DNA
1µL
6. Test E DNA
1µL
7. Test F DNA
1µL
8. Test G DNA
1µL
Taq polymerase enzyme
1µL
1µL
1µL
1µL
1µL
1µL
1µL
1µL
2. These tubes were put into the PCR machine to heat and cool to 95°C, 55°C and 74°C for 30 cycles. The
enzyme Taq will copy the section of the ACTN3 gene for each person. To detect the X mutation the
PCR fragments are then cut with the Dde I restriction enzyme.
3. The R (normal ACTN3 gene) gives one band and the X (mutant ACTN3 gene) gives two bands due to
the presence of the Dde I cutting site.
4. The PCR and restriction digests have been done for you. You will separate the bands on a DNA
electrophoresis gel in the lab today.
5. DNA electrophoresis to separate the bands from the PCR: Pipette the samples into the wells of the
agar gel in the order indicated below. Run the gels to separate the samples. Take a photo of the result.
1. Control R/X
2. Test A
3. Test B
4. Test C
5. Test D
6. Test E
7. Test F
8. Test G
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AFTER THE LAB:
Decide on the ACTN3 genotype from your gel results and write it down.
Note ideas on whether this type of testing is useful
Note ideas on any issues it may raise
FOR INTEREST: What is polymerase chain reaction (PCR)?
PCR copies defined pieces of DNA sequence so there is enough to study in the laboratory.
Two short DNA primers define the piece copied – these mark the start and end of the piece.
The copying is done by Taq polymerase – an enzyme that joins the A, G, T& C’s according to the template
sequence of the sample DNA.
Temperature is used to control the reaction:
♦ 95°C first separates the two strands of DNA
♦ 55°C the primers bind to each strand
♦ 74°C Taq enzyme adds bases to the primer following the sample DNA template
This pattern of heating & cooling repeats for 30 cycles = billion fold copying of the DNA segment
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