Year 10 Biological Science
ANALYSIS OF A GENETIC CROSS
INTRODUCTION: Inheritance Patterns in Barley Plants
The green colour in plants comes from a pigment called chlorophyll. Chlorophyll is needed for
photosynthesis where it traps energy from the sun and uses this to build a sugar energy in a cell.
Normal barley plants have a green colour which means they have alleles that code for the
production of the pigment chlorophyll. In some plants, a mutant allele occurs. If a plant processes
two copies of the mutant allele, it will not be able to produce chlorophyll and will therefore be
white.
In an experiment a pure breeding green plant was crossed with a pure breeding white plant. All of
the F1 generation were green. The seeds of these plants were germinated and allowed to grow
and produce seeds. When these seeds are planted they will be the F2 generation.
P Generation
(pure breeding)
F1 generation
F2 generation
X
In this experiment you will be growing the F2 generation seeds. When these plants have grown
you will be able to observe their phenotype and you can compare your results with the expected
value.
Aim:
To investigate the inheritance pattern of green versus white barley plants.
Equipment
Petri dishes
Barley seeds (20 per group)
Cotton wool
Method
1. Place some cotton wool in a Petri dish and soak it with water.
2. Place 20 barley seeds on the cotton wool and leave them for about 4 days or until the
seedlings are about 5-10cm tall. Remember to keep the cotton wool moist, but don’t over
water them.
3. After the seedlings have germinated count the number of white and the number of green
seedlings and record your results in the table provided below.
4. Obtain the results of the other groups in the class and also record them in the table below.
Use the table below to record the data obtained from completing the experiment.
Results
GROUP
Number of
Green Barley
Number of
White Barley
SAMPLE SIZE
PERCENTAGE
Green
Discussion Questions:
Question 1
Use the information provided to write appropriate symbols for both alleles.
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Question 2
Write down all of the possible genotypes for:
Green plants __________________________________________________________________________
PERCENTAGE
White
White plants __________________________________________________________________________
Question 3
Explain how the phenotype of the F1 generation can be used to establish which trait is dominant
and which is recessive.
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Question 4
Show all of the necessary working required to predict the genotypic and phenotypic ratio of the F2
generation.
Question 5
Compare the results your group obtained to those predicted in the question above. Explain why
experimental results can differ from expected results.
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Question 6
Use the experimental data gained from your class to explain why it is important to use the class
results rather than the data produced by an individual group.
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Question 7
A farmer wanted to establish a pure breeding line of green Barley plants. The problem is that a
green barely plant could be homozygous or heterozygous. Outline an experiment you could do to
identify a heterozygous green plant from a homozygous green plant.
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Conclusion
Write a short statement summarising the main findings from this experiment.
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