Higher task HB2.25.1
Lesson reference: B2.25 The importance of Mendel’s
work
The importance of Mendel’s work
Learning objectives:
 Know that other scientists rediscovered Mendel’s work and linked his
‘inherited factors’ with chromosomes and genes.
 Understand that there are different forms of genes, called alleles.
 Be able to interpret genetic diagrams of monohybrid inheritance.
Suggested time:
30 minutes
Name: ________________________________ Date: ______________________
Read the following passage and then answer the questions.
Gregor Mendel carried out many plant breeding experiments and worked out
some laws of heredity. He worked in the garden of his monastery and carried out
breeding experiments with pea plants, Pisum sativum.
He understood the structure of flowers and that he could remove the anthers of
some of the pea flowers before they were mature. This emasculated the flowers,
that is, removed their male parts. He could then take pollen from another pea
flower and, using a small brush or a feather, place it on the stigma, the female
part of a pea flower.
Pea plants were particularly useful because they have the following
characteristics:
 There are many distinct varieties of them, with distinct phenotypes.
 These different varieties belong to the same species and they can be interbred
to produce fertile offspring.
 The flowers normally self-pollinate but can be crossed, as described above.
 The plants are easy to grow.
 They have a one-year life cycle so Mendel could collect data relating to many
generations.
One type of pea plant has flowers all along the stems. This is called axialflowering. Another type of pea plant has flowers only at the ends of stems. This is
called terminal-flowering. Other plant breeders had carried out experiments
similar to the ones Mendel did, but Mendel was the first to count the different
types of offspring and collect numerical data.
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Mendel crossed true-breeding, axial-flowered plants with true-breeding terminalflowered plants. He collected and grew the seeds. All the F1 generation produced
plants with axial flowers.
He allowed these plants to self-pollinate, and therefore self-fertilise, and collected
and grew their seeds. In the F2 generation, there were 858 plants. 657 of them
were axial-flowered.
A Which characteristic is dominant – axial flowering or terminal flowering?
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B In the F2 generation, how many of the offspring have terminal flowers?
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C How did Mendel make sure that none of the true-breeding pea parents could
self-pollinate?
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D How did Mendel cross pollinate the two types of pea plant?
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E Draw genetic diagrams, using Punnett squares where necessary, to explain
the results described above. Show the phenotypes and genotypes of the
parents and offspring. Indicate whether individuals are homozygous or
heterozygous.
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F As Mendel worked in a monastery garden, where food plants were grown, it
may have been luck that he worked with pea plants. What characteristics of
pea plants made them very useful for his breeding experiments?
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G Pea plants have 14 chromosomes in each of their body cells. How many
chromosomes are there in i a pea male gamete, ii a pea female gamete?
i _________________________
ii __________________________
H What type of cell division is used to make pea gametes?
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I
Although Mendel’s work, which was published in 1866, was not recognised for
its great importance at the time, Mendel is now revered amongst biologists and
geneticists. Biologists describe characteristics that are determined by a single
gene that has two or more alleles as Mendelian. Their inheritance pattern is
also described as Mendelian. Some human traits that show simple Mendelian
inheritance include ear lobe shape, tongue-rolling, sickle cell disease, cystic
fibrosis, and Huntington disease. There are many other traits, such as arthritis,
which involve many genes, so they do not show such a simple inheritance
pattern.
Which type of inheritance pattern could a genetic counsellor most easily
explain to a couple expecting a baby?
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J In the USA, between 1904 and 1925, a biologist called Thomas Hunt Morgan
carried out many genetics experiments. He put forward the idea that genes
and chromosomes contain the inheritable material that determines an
organism’s characteristics and development. Along with three other biologists,
he rediscovered Mendel’s work and realised its significance. He also realised
that understanding how genes and chromosomes work gave the support to
Darwin’s theory of natural selection needed to explain the phenomenon of
evolution.
Which one of the following statements do you think is untrue?
1 Mutations cause changes to an organism’s genetic material – genes or
chromosomes.
2 Mutations can be passed on to offspring.
3 Some mutations are useful and make an organism better adapted to its
environment so it can out-compete other organisms of its species.
4 Evolution is a fact as new species have arisen since life began on Earth.
One theory that can explain how this happened is the theory of natural
selection, put forward by Charles Darwin. This is the most widely accepted
theory as there is a lot of scientific evidence to support it.
5 Scientists cannot be sure that genes and chromosomes are the hereditary
material of living organisms.
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