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Level 3-8
(AF 1.3)
Gregor Mendel and his obsession with pea plants!
Who was Gregor Mendel?
Gregor Mendel was born in 1822. He was the son of a poor farmer. In order for him
to get an education he joined the church and became a Monk.
While at the monastery, Mendel became interested in mathematics and biology and
began to teach biology at the university. However, Mendel found teaching the ideas
of inheritance very difficult. He had to teach his students a theory called ‘The
Blending Theory’. This was the idea that offspring were a perfect blend of both
parents. However, he began to realise that the blending theory was flawed as it
could not explain how a black sheep could be born from two white parents and how a
blue eyed child could be born from parents with brown eyes. He set out to find out
what caused inheritance.
What did he set out to find out?
The flaws that Mendel could see in the blending theory made him determined to
investigate what caused inheritance. He needed a living thing that was easy to
reproduce and to count. This was when his attention turned to peas! He could cross
pollinate different strains of pea plants and count the characteristics seen in the
offspring produced. His experiments could be easily reproducible by others. Surely
no-one could argue with the findings?
His experiments
Mendel carried out many breeding experiments with peas. He bred pure strains of
peas together. In one of his experiments, he bred round pea plants with wrinkled
pea plants.
He found that all the
offspring were round!
Mendel then bred the offspring together.
He found that exactly ¾ of the offspring were round and a ¼ were wrinkly.
This demonstrated that round peas were more common than wrinkled peas in the
offspring. However, it also showed that the information for a wrinkled pea seemed
to be passed on even when the parents were not wrinkled themselves. This
characteristic was seen in later generations. Mendel suggested that characteristics
were passed on from parents to offspring in ‘inherent material’ and that some codes
of this inherent material were stronger than others i.e. more dominant. The weaker
genes are said to be recessive and two recessive genes are needed for a recessive
characteristic to be seen. This is why only ¼ of the second generation peas were
wrinkly. They inherited two recessive genes coding for a wrinkly surface.
In previous lessons, you have seen how you can use genetic crosses to work out the
chances of the offspring having a certain characteristic. Below is a genetic cross
showing the two genes of each parent from the second generation of plants. It
shows that 25% of the offspring would be wrinkly, while 75% will be smooth. This is
exactly what Mendel’s experiments found out.
Parent’s
genes
w
S
w
ww
Sw
S
Sw
SS
Reasons why no one believed him
Mendel’s ideas were flatly rejected by the scientific community. He held a seminar
explaining his experiments and the results to the scientific community. However,
everyone left the seminar before it even ended.
Here are some reasons why his ideas of inheritance were not believed
 People did not know what determined our characteristics as they did not know
about chromosomes, genes or DNA. Mendel was lacking any evidence of what
was actually being passed on from parents to offspring.
 The church was very strong and Mendel’s ideas were not readily accepted by
the church.
 Mendel’s presented his findings in complicated mathematical ways which no one
could understand and so they felt like they were in a complicated mathematics
lesson rather than a seminar on what causes inheritance.
 Most of the scientific community believed in the blending theory. This was the
idea that you were a blend of your parents.
 Scientists argued that peas were plants and were much simpler organisms than
animals. For this reason, they said that inheritance in peas was unlikely to be
anything like the mechanisms of inheritance in animals.
What you need to do
Complete the following on the sheet provided
Level 3
What question was Mendel trying to answer when he carried out his experiment
with pea plants?
Using the information given, give two reasons why pea plants were a good living
thing to use to answer this question
Level 4
Mendel cross-pollinated one type of pea plant with another. Cross-pollination is the
same as fertilisation in animals. In animals the sperm and egg join together to form
a fertilised egg cell which then grows to form an embryo (unborn baby).
1. Use the information above about animal fertilisation and the labelled
diagram of a flower from a pea plant to explain how Mendel cross-pollinated a
smooth pea plant with a wrinkled pea plant to form a seed.
You should use the following key words in this description: pollen, stigma, ovary,
seed
Level 5
1. A lot of people would say that Mendel’s thinking was creative. Suggest reasons
why people may think that Mendel was a creative thinker. Use the information in
the passage to help you with this!
2. What evidence did Mendel use to back up his theory of inheritance? Do you
think this was strong or weak evidence and why?
Level 6
In a much detail as you can suggest reasons why people now believe Mendel’s theory
of inheritance to be true
Level 7
1. In as much detail as possible, explain why the Blending theory is now widely
rejected by the scientific community
2. In as much detail as possible, explain what advancements in technology and
evidence have led to Mendel’s theory being widely accepted by the scientific
community.
Level 8 (application of knowledge)
A scientist suggests that the birth of a child is triggered by a hormone released
from the breasts in the last few months of pregnancy. In as much detail as you can
explain how this theory would be accepted or rejected by the scientific community.
Scaffolding to help them with this
To do
PowerPoint for teacher to go over the concepts for students with literacy issues
Modify to allow access for less able as this is high level!!!!!!!!!!!!!!