Transcript HHMI NSTA Presentation 2016 v2 - tguilfoyle

Tim Guilfoyle
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[email protected]
Phillip O. Berry Academy
Charlotte, NC 28075
Using Genetic Crosses to Analyze a
Stickleback Trait
• Is one phenotype (with spines or without spines) dominant and one
recessive?
• Students apply the principles of Mendelian genetics to analyze the
results of genetic crosses between stickleback fish with different traits,
or phenotypes (with and without spines).
• Students will use photos of actual research specimens to obtain their
data; they will then analyze additional research data from the scientific
literature.
The fish shown in the photo on the left is a marine
threespine stickleback. Like all marine
stickleback, this fish has a pair of pelvic spines
(only one is visible), which serve as a defense
from large predatory fish. In some freshwater
populations stickleback lack pelvic spines. (The
scale is in centimeters.)
The Making of the Fittest: Evolving Switches, Evolving Bodies
The Making of the Fittest:
•
•
•
•
Evolving Switches, Evolving Bodies
Freshwater stickleback populations
were established when marine
populations became trapped in lakes,
initially connected to the ocean, that
formed at the end of the last ice age.
Freshwater stickleback fish underwent
many “changes” (color, size, skeleton)
as they adapted to life in freshwater.
The presence of different predators in different lakes dictated the
subsequent evolution of each isolated lake stickleback over the course
of about 10,000 years.
Some groups “kept” their spines to use against predatory fish while
others “lost” their spines, perhaps to evade aquatic insect predators.
The Making of the Fittest: Evolving Switches, Evolving Bodies
In the ocean there are
lots of large predatory
fish and there is no
place to hide.
The Making of the Fittest: Evolving Switches, Evolving Bodies
The Making of the Fittest: Evolving Switches, Evolving Bodies
They’re generally easy
for predatory fish to
catch but they’re not
easy to swallow.
The Making of the Fittest: Evolving Switches, Evolving Bodies
Using Genetic Crosses to Analyze a Stickleback Trait
Stating the Hypothesis: Which Phenotype Is Dominant? Examine
the offspring of a genetic cross between a stickleback from the ocean
(marine stickleback) and a freshwater stickleback from Bear Paw Lake.
1.
Based on what you learned in the film, what are the phenotypes of
these two parental stickleback fish? Indicate your choice with a
check mark.
Marine
__ pelvic spines present
__ pelvic spines absent
Bear Paw Lake
__ pelvic spines present
__ pelvic spines absent
2.
If we start with the simplest assumption that the presence or
absence of pelvic spines is controlled by a single gene with two
alleles, how would you denote the genotype of the two
homozygous parents?
PP X pp
What is your hypothesis for which phenotype is dominant and which one is recessive?
Assign Genotypes:
PP or pp
Marine __________________
PP or pp
Bear Paw Lake _________________
Based on your hypothesis, what would you expect to
be the results of the cross between the Marine and
Bear Paw Lake stickleback parents?
Answer depends on which phenotype is hypothesized
to be dominant (with spines or without spines); however
100% of F1 will be heterozygous (1:0 ratio)
What do you expect would be the result of crossing two
F1 fish to produce the second filial (F2) generation?
3:1 ratio
If you had 40 offspring in the F2 generation, approximately how many would you expect
to have pelvic spines and how many to lack pelvic spines?
30 : 10 (with spines and without spines or vice versa depending on the students hypothesis)
Obtaining the Data: Do the Results from the
Experiment Support Your Hypothesis?
• Now you will use the fish cards to see whether the result of
the crosses described support your hypothesis.
• The cards show photographs of stickleback fish that were
stained with a solution that turns bones red, making them
easier to see.
• There are two sets of cards: the first set (16 cards) represents
the F1 generation and the second set (40 cards) the F2
generation.
• You will be sorting these cards according to whether the fish
have pelvic spines.
A stickleback with pelvic spines. The fish is shown in side(lateral) and
belly (ventral) views, and the pelvic spines are indicated by the arrows. The pelvic
spines are attached to the pelvic girdle.
A stickleback without pelvic spines. The fish has a reduced pelvic girdle
(indicated by the circles) with no pelvic spines attached to it.
Sort the F1 set of cards into two separate piles: fish with pelvic spines and fish without
pelvic spines. Count and record the total number of fish with each phenotype in the table
below. What is the ratio of fish with pelvic spines to fish without pelvic spines in the F1
generation?
*
16
0
1:0 Ratio (all sticklebacks have pelvic spines)
Repeat the same procedure with the F2 set of cards. Count and record the total number
of fish with each phenotype in the table below.
31
9
Which fish have no spines?
3:1 (3.4:1) Which trait is dominant?
Extensions:
Do these results support the hypothesis
that the presence or absence of pelvic
spines is controlled by a single gene?
Explain using evidence.
What
is
fitness?
Tim Guilfoyle
[email protected]
tguilfoyle.cmswiki.wikispaces.net/
Phillip O. Berry Academy
Charlotte, NC 28075
HHMI Ambassador
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“Life moves pretty fast. If you don't stop and look around
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Extension: Analyzing Additional Experimental Data
(Do the results agree?)
Crosses Between Several Marine and Freshwater Stickleback: The F1 Generation
*
Students should realize that although the numbers are
different, their results are consistent with the crosses shown.
In both cases, all fish in the F1 generation had pelvic spines.
Extension: Analyzing Additional Experimental Data
(Do the results agree?)
Crosses Between F1 Generation Stickleback from the Marine x Bear Paw Lake
You will notice that the phenotype ratios vary from family to family. Explain why
every family does not show the same ratio.
WHY??????
Further Extension: Chi Square Statistics
The null statistical hypothesis for the F2 generation is that the observed outcome
of 351 fish with pelvic spines and 97 fish without pelvic spines is not significantly
different from the expected 3:1 ratio; any deviation from the expected 3:1 ratio
likely occurred by chance alone.
Total Fish Population:
df = 2 − 1 = 1
Since p > 0.05, we cannot reject the null hypothesis. This result suggests that
the difference between the observed and expected data is not statistically
significant; this difference is thus likely to be solely due to chance.
The Making of the Fittest:
Film Introduction:
Evolving Switches, Evolving Bodies
• Freshwater stickleback populations were
established when marine populations became
trapped in lakes, initially connected to the ocean,
that formed at the end of the last ice age.
• Freshwater stickleback populations are very
different from marine populations because they
have adapted to life in freshwater environments.
• Freshwater stickleback fish underwent many
changes (color, size, skeleton) as they adapted
to life in freshwater.
• This activity focuses on changes in the pelvic
skeleton because this trait is highly variable and
is easy to see and measure.
• The underlying genetic mechanisms are well
studied too.
The Making of the Fittest:
Film Introduction:
Evolving Switches, Evolving Bodies
• Freshwater stickleback populations were
established when marine populations became
trapped in lakes, initially connected to the ocean,
that formed at the end of the last ice age.
• Freshwater stickleback fish underwent many
“changes” (color, size, skeleton) as they adapted
to life in freshwater.
• This activity focuses on changes in the pelvic
skeleton because this trait is highly variable and
is easy to see and measure.
• The underlying genetic mechanisms are well
studied too.
It changed your teaching and you don't
know how your students learned
without it?
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