Variation and
Inheritance
WJEC Biology Module 1
2011 Specification
Variation
WJEC Biology Module 1
2011 Specification
Learning Outcomes
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Examine the variation in height/length in
individuals of the same species by
collecting and analysing data and know
that variation may be due to
environmental or genetic causes.
Understand that variation may be
continuous or discontinuous.
Keywords
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Clones
Fertilisation
Inheritance
Chromosome
Exposure
Gamma rays
Mutation
Ultraviolet radiation
X-rays
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Continuous
Discontinuous
Environmental factors
Genes
Mutation
Phenotype
Variation
Sexual reproduction
Asexual reproduction
Variation

Look at variation in the class

Try to write down at least 20 ways in which
individuals vary from one another.
Variation
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Variation can be described as either
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Continuous variation
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a range of measurements from one extreme to the
other. E.g. height
Discontinuous variation
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individuals fall into distinct categories. E.g. ability to
roll the tongue; attached or free ear lobes
Continuous variation
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Use a tally chart and plot results in a
histogram
Discontinuous variation
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Plot results in
a bar chart
Variation
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Differences in the characteristics of
different individuals of the same kind may
be due to differences in
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The genes they have inherited – genetic
causes
The conditions in which they have developed
– environmental causes
Variation is normally a combination of
both genes and the environment.
Phenotype
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The phenotype is the outward
appearance of an organism
It depends on both the organism’s genes
and its environment.
Variation in Snails - Practical
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Snails of two closely related species of
Cepaea are common in woodland and
grassland in Britain.
They show a pattern of variation known
as polymorphism.
This means that there are several different
‘types’. The shell may be either yellow or
pink/brown, and it may have dark stripes
or be plain.
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So, the four types of
the snails are as
follows:
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Pink/brown, plain
Yellow, plain
Pink/brown, striped
Yellow striped
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Even within each
type, there is
variation, so that the
pink/brown variety
may be distinctly
pink, or brown, or
even greyish, and the
striped forms may
have different
numbers of stripes, for
instance.
Variation in Snails - Practical
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Pick 50 snails at random for the grassland
Use the table to create a tally chart
recording the number of each type of
snail found in the grassland
Write your results onto the main table
Calculate the percentage of each snail
type
Repeat the stages above for woodland
snails
Conclusion
1. What differences do you notice in the
distribution of the different types of snail?
Describe any trends seen. [2]
2. Describe one difficulty in the method that
might have reduced the accuracy of the
results [1]
3. The size of the sample can affect the
accuracy of the results. In using a sample, do
you think a sample size of 50 was big enough?
Give a reason for your answer
Evaluation
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Plan a similar activity to find out if the
snails grow bigger in woodland or
grassland.
Describe, in detail, the procedure you
would use.
Suggest any difficulties you may have in
obtaining valid results
Suggest how these difficulties may be
avoided.
Learning Outcome
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Understand that sexual reproduction
leads to offspring that are genetically
different from the parents unlike asexual
reproduction where genetically identical
offspring called clones are produced
from a single parent. Sexual reproduction
therefore gives rise to increased variation.
Genetic Variation
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Sexual reproduction
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Egg and sperm fuse at fertilisation, to form a
zygote
The zygote has a set of genes from the
mother and a set from the father.
Offspring are genetically different from their
parents
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Asexual reproduction
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No fertilisation, no mixing of genes
Offspring are genetically identical to each
other and the parents
Produces clones
Cloning
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Cloning can be used to mass produce
economically important organisms
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Animals
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IVF – In vitro fertilisation
Plants
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micropropagation
Prep
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WJEC Science Page 34
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What are continuous and discontinuous
variation?
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Question 1
Inheritance
WJEC Biology Module 1
2011 Specification
Learning outcomes
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Understand that genes are sections of DNA
molecules that determine inherited
characteristics and are in pairs. Genes have
different forms, called alleles.
Know that chromosomes are linear
arrangements of genes and that chromosomes
that are found in pairs in body cells are strands
of DNA. DNA contains coded information for
the production of different types of proteins.
These proteins determine how cells function.
Chromosomes and Genes
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Our cells contain genetic information this
is your DNA.
This information on DNA is in units called
genes.
Our genes are on chromosomes.
Chromosomes always come in pairs in
our body cells.
Genetics and DNA
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Each chromosome is made up of
thousands of genes;
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the genes carry genetic information that
affects how we grow and what we look like.
A chromosome is made up of a long
thread, made up of deoxyribonucleic
acid (DNA).
One gene is made up of a short length of
DNA.
DNA
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DNA is twisted into a
double helix, where bases
pair up:
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Adenine with thymine
Guanine with cytosine
Every 3 bases along the
strand codes for a
particular amino acid,
this means that DNA
controls the proteins that
are made
DNA and Genetics
GCSE Practical
What is DNA?
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DNA is packed tightly into chromosomes inside
the cell, it is a gigantic molecule, very long but
very thin.
DNA from a single cell can be 2 metres long,
but is so thin that it can hardly be seen with a
powerful microscope.
When DNA is released from cells it clumps
together to form strands, which are colourless
and jelly like.
Extraction of DNA from cells is the first step in
many experiments in genetic engineering. DNA
can be extracted from both plant and animal
cells.
How to extract DNA
from kiwi fruit!
Equipment
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Kiwi fruit
White tile
Scalpel
Tap water
Warm water 600C
Ice cold ethanol
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Washing up liquid
Coffee filters
Plastic measuring
cylinders
Funnels
250ml beaker
Boiling tube
Boiling tube bung
Method – Stage 1
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DNA extraction mixture:
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Finely chop the kiwi fruit and place in
boiling tube.
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Mix 10ml washing up liquid + 3g salt + 100ml
water in a 250ml beaker
add DNA extraction mixture
Place bung on top and shake carefully.
Leave for fifteen minutes at 60oC
Method – Stage 2
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Filter the mixture through the coffee filter into a
100ml beaker to separate the chopped kiwi fruit
from the clear liquid. (the DNA is invisible as it is
dissolved in the clear liquid)
Transfer 5 ml of the clear liquid into a clean test
tube.
Add 5ml of cold (4oC) absolute alcohol down
the side of the tube.
DNA will appear as “fluffy” white solid.
Final “tricky” stage
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The DNA can be
pulled out using a
fine wire.
Learning Outcomes
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be able to understand and complete
Punnett squares and explain the
outcomes of monohybrid crosses
including ratios.
The following terms should be
understood:
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genotype, phenotype, dominant, recessive,
F1, F2, selfing, heterozygous, heterozygote,
homozygous and homozygote
An understanding of simple Mendelian ratios.
Inheritance
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Things to remember:
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Chromosomes are strings of genes and
chromosomes occur in pairs in each cell.
There are two copies of each gene in each
cell
These genes may be identical or may be
different versions (alleles) of the same gene.
Glossary
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Homozygous
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Heterozygous
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2 different alleles for a particular characteristic
Genotype
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2 identical alleles for a particular characteristic
alleles for a particular characteristic
Phenotype
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outward effect of those alleles
Glossary
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Dominant
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allele which controls the
development of a
characteristic when it is
present on only one
chromosome.
Recessive
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allele which control the
development of a
characteristic if present
on both chromosomes.
Further definitions
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F1 – first generation
F2 – second generation
Selfing
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Manually pollinating a flower by placing its
pollen on its own stigma
Self pollination
Monohybrid Inheritance
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The study of how a single gene is passed
on from parents to offspring.
A punnet square can be used to predict
an outcome
Genetic Cross - Tips
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When you write out a genetic cross, make sure
you state what the symbols represent
Make sure you label each line in the cross
(phenotype, genotype, etc)
It is a good idea to circle the gametes to show
that meiosis has happened
Read the question carefully – are you asked to
state the outcome in terms of the genotype or
the phenotype?
A cross between a pure-breeding tall pea plant
and a pure-breeding dwarf pea plant
A cross between two F1 pea
plants
A cross between a heterozygous tall
pea plant and a dwarf pea plant
Now try this …….
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You need to be able to predict the genotypes
of the parents from descriptions of them.
Work out the following genotypes, based on
peas that can be round or wrinkled, with round
being dominant to wrinkled.
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A heterozygous round pea
A wrinkled pea
A pure-breeding round pea
Learning Outcomes
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Understand that most characteristics are
controlled by more than one gene.
consider the scientific process of
observation, experimentation and
deduction that led Gregor Mendel to
propose the mechanism of inheritance.
Discuss why the significance of the work
was not recognised and validated by
scientists for many years.
Gregor Mendel
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Gregor Mendel was a monk who did
experiments looking at the inheritance of
height in pea plants.
He did not publish any of his results in
scientific journals, so no one took any
notice of his work during his lifetime.
He is now regarded as one of the
greatest scientists of all time.
Learning Outcome
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know that in human body cells, one of
the pairs of chromosomes, XX or XY,
carries the genes which determine sex.
These separate and combine randomly
at fertilisation.
Inheritance of Sex in humans
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The sex chromosomes X and Y determine
the sex of an individual
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Males
Females
XY
XX
The presence of the Y chromosome
results in male features developing
Inheritance of sex
Learning Outcomes
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understand that when gametes are
formed the chromosome number is
halved and the genetic composition of
the daughter cells is not identical (the
term, meiosis, and knowledge of stages
are not required). Fertilisation restores
normal chromosome number.
Chromosomes and Genes
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Human body cells have 23 pairs of
chromosomes. This gives a diploid
number (2n) of 46.
Human gametes contains 23
chromosomes, this is the haploid number
(n).
Pupil Activity
Copy and complete the following sentences.
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Another name for sperm and egg cells is
.
These sex cells join to make one cell, the
_____________.
This cell grows into a foetus by
___________
many times. Each body cell in the baby contains
pairs of chromosomes.
One of the chromosomes in each pair comes from
the
, the other chromosome in each
pair comes from the
.
Human Life Cycle
Diploid
Zygote
46
fertilisation
Cell Division
Number of chromosomes
Mitosis
Haploid
Sperm
23
Haploid
Egg
23
Meiosis
Adult
46
Learning Outcomes
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understand that new genes result from
changes, mutations, in existing genes and
that mutations occur at random. Most
mutations have no effect but some may
be beneficial or harmful. Mutation rates
can be increased by ionising radiation.
(Reference to specific ionising radiation is
not required.)
Mutations
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A mutation is a change in the structure of a
gene
Mutations are
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Rare
Random
They can have
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No effect
beneficial effects
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If a mutation improves the “design” of an organism this
can lead to increased survival.
harmful effects
Causes of Mutations
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Mutations can occur naturally
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Mutations rate can be increased by
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Ionising radiation
X-rays
chemicals
Learning Outcomes
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understand that some mutations cause
conditions which may be passed on in
families, as is shown by the mechanism of
inheritance of cystic fibrosis, and be able
to interpret family trees.
Inherited Diseases
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Genetic diseases can be caused by:
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Dominant or recessive alleles on normal
chromosomes
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E.g. cystic fibrosis (recessive), Huntington’s Chorea
(dominant)
Recessive genes on X chromosome
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E.g. haemophilia
Cystic Fibrosis
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This is the commonest inherited disease among white
people; it affects one in every 2000 children. In a
person with the disease thick, sticky mucus builds up in
respiratory passages and digestive glands, making the
person susceptible to infection and disrupting digestion.
Cystic Fibrosis
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This is a disorder of cell membranes;
it is caused by a recessive allele of a gene.
It must be inherited from both parents.
As it is a recessive allele parents may be carriers
of the disorder without actually having the
disorder themselves.
Pupil Activity
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Let N = normal allele
Let n = allele for cystic fibrosis
Carry out the following crosses and work
out the chances of a child having cystic
fibrosis for each cross.
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Nn x Nn
NN x Nn
Pupil Activity
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Cystic fibrosis and family tree w/sheet
Learning Outcomes
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Discuss the issues surrounding the
development and use of gene therapy
which has been tried as a means to
alleviate the symptoms in cystic fibrosis
sufferers but has greater potential as
advances are made in knowledge and
technology.
Learning Outcome
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understand that an organism's DNA can be
analysed by 'genetic profiling' and how this can
be used to show the similarity between two
DNA samples.
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The process involves cutting the DNA into short pieces
which are then separated into bands.
The pattern of the bands produced can be
compared to show the similarity between two DNA
samples, for instance in criminal cases, paternity cases
and in comparisons between species for classification
purposes.
Advances in technology now make such analysis
widely available.
Genetic Profiling
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Genetic profiling is a method by which
an organism's DNA can be analysed
this can be used to show the similarity
between two DNA samples.
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The process involves cutting the DNA into
short pieces
These are then separated into bands.
The pattern of the bands produced can be
compared to show the similarity between two
DNA samples
Stages in genetic profiling
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Collect a sample of cells
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E.g. blood, hair follicles, semen, skin
Break cells up and extract DNA
Enzymes are used to break the DNA into
segments of differing sizes.
Gel Electrophoresis
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DNA fragments are placed on a gel
Electric current is passed through the gel
Smaller fragments move further through the gel
The pattern that develops is the genetic profile.
Learning Outcome
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Discuss the benefits of DNA profiling, for
example to identify the presence of certain
genes which may be associated with a
particular disease. As this likelihood may be
based on statistical probability, understand that
it raises issues such as risk-benefit considerations
and disclosure of information along with wider
ethical issues of ownership and human rights
which are subject to value judgement by
society.
Uses of Genetic Profiling
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A genetic profile is a pattern of bands or lines
It is unique to each individual and can be used
to identify an individual person.
For example
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Identification of a suspect in a crime
Identification of a dead body
Look for genetic relations
 Maternity
 Paternity
Species identification for classification
Is genetic profiling a good thing?
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What are the benefits of DNA profiling?
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to identify the presence of certain genes which may
be associated with a particular disease.
Problems with this
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As this likelihood may be based on statistical
probability
understand that it raises issues which are subject to
value judgment by society.
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risk-benefit considerations
disclosure of information along with wider ethical issues
of ownership
human rights
Learning Outcomes
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know that genes can be transferred
artificially from one species to another.
Genetic Modification
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Genetic modification is the process by
which a gene is taken from a
chromosome of one species and put into
a chromosome of another species
For example
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Genes inserted into crop plants so that they
produce an insecticide, making the plants
resistant to pests
Learning Outcomes
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Understand that the introduction of
genes from herbicide-resistant plants into
soya bean plants, so increasing their
resistance to herbicides, may increase
the crop yield due to reduced
competition.
Herbicide resistance
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A common feature of genetically modified
crops is resistance to herbicide.
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A herbicide resistant gene is transferred from a soil
bacteria and transferred to Soya bean plants
Advantages of herbicide resistance in Soya
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Increases herbicide resistance, so farmers can kill
weeds without damaging crop plants
Removing weeds reduces competition for the crop
improving crop yield
Learning Outcomes
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Understand the potential disadvantages
and issues involved.
GM Crops and developing
countries
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Advantages
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Crops tailor made to suit the farming conditions
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More nutritional value
Higher income
Energy-producing crops could save natural resources
Disadvantages
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GM crops in developed countries mean that they no
longer need to import from abroad – developing
countries lose trade
Mismanagement and political reasons
Problems with GM Crops
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All issues raised with GM crops raise
important political, ethical and trade
questions.
Learning Outcomes
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investigate and evaluate the potential benefits
and problems posed by advances in GM crop
technology
Understand the need to collect reliable data,
e.g. the use of farm scale field trials, in order
that possible effects on the environment and on
health should be understood. The data may be
used to help formulate policy decisions
regarding the planting of these crops and to
inform consumers.
Learning Outcomes
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Understand the need for unbiased
information and interpretation as it
affects the public perception of foods
containing GM products and informs risk
management considerations of possible
consequences.
Activity
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Read through the sources provided
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Comment on whether these sources are
biased or unbiased
Make notes on any facts that you think are
important
Write a short evaluation on the advantages
and disadvantages of GM Crops