24'1 What is genetics

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24 Genetics

• 24.1 What is genetics?
• 24.2 Genes and inheritance
• 24.3 The pattern of inheritance
• 24.4 Variations
• 25.5 Inherited disorders in humans (Extension)
• 25.6 Genetic engineering
• Mind Map

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24.1 What is genetics?
What is
genetics?
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24.1 What is genetics?
Heredity
Passing on characteristics from one generation to
the next
Variation
The differences between individuals of the same
species
The study of how characters are transferred or
inherited from one generation to the next
Genetics
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24.2 Genes and inheritance
Genes

inheritance
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24.2 Genes and inheritance
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Nucleus
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24.2 Genes and inheritance
DNA (deoxyribonucleic acid)
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24.2 Genes and inheritance
forms part of a chromosome
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24.2 Genes and inheritance
Chromosome
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24.2 Genes and inheritance
Gene is a short length of DNA
can determine a specific character of an organism
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24.2 Genes and inheritance
Allele 1
Allele 2
Allele 1
Gene 1
Allele 2
Different color
Alleles
the alternative forms of a gene
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24.2 Genes and inheritance
Human Genome Project (HGP)
Genome is ALL the genes of an organism
Mapping the base sequence of the human genome
Aim
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24.2 Genes and inheritance
Human Genome Project (HGP)
Applications
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Improved diagnosis of disease
Gene therapy
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New energy sources (biofuels)
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Environmental monitoring to detect pollutants
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24.2 Genes and inheritance
Human Genome Project (HGP)
Applications
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Safe, efficient cleanup of toxic waste
Study of evolution and mutation
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Develop disease-and-insect-resistant crops
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Develop healthier, more productive and
disease-resistant farm animals
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24.2 Genes and inheritance
Human Genome Project (HGP)
Drawbacks
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Expensive time-consuming
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Problem of ownership
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24.3 The pattern of inheritance
The pattern of
inheritance
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24.3 The pattern of inheritance
Mendel is known as the father of genetics
He carried out a series of breeding experiments
on garden pea
which were easily grown have easily
identifiable characteristics
Gregor Mendel (1822-1884)
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24.3 The pattern of inheritance
Mendels breeding experiment
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anthers are removed to prevent self-pollination
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pea flower bud
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pollens from other plant was taken were dusted
onto the stigma, resulting in cross-pollination
wait until the stigma was ready to receive pollen
enclosed the flower with a bag to prevent further
pollination
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24.3 The pattern of inheritance
Mendel studied the inheritance of just ONE pair
of contrasting characteristics (traits) of pea
plants each time
Monohybridinheritance
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24.3 The pattern of inheritance
X
Parents (pure-breeding)
short
tall
Why?
First filial (F1) generation
all tall
self-pollination
Tall Short
3 1
Second filial (F2) generation
277 short
787 tall
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24.3 The pattern of inheritance
If pure-breeding parent is tall, it means
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two alleles are identical
control the same feature (tall)
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24.3 The pattern of inheritance
Let T be the allele for being tall
The alleles for pure-breeding tall parent are TT
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24.3 The pattern of inheritance
pure-breeding parent is short
Let t be the allele for being short
The alleles for pure-breeding short parent are tt
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24.3 The pattern of inheritance
Express Tall Only
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24.3 The pattern of inheritance
Express Short Only
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24.3 The pattern of inheritance
Short
Tall
P
TT x tt
A pure-breeding tall plant
crosses with
a pure-breeding short plant
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24.3 The pattern of inheritance
G
T
T
t
t
When gametes are formed by meiosis, the
homologous chromosomes separate
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24.3 The pattern of inheritance
T
t
Just show the possible types of gametes produced
When gametes are formed by meiosis, the
homologous chromosomes separate
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24.3 The pattern of inheritance
T
t
Tt
F1
Tall
All F1 are tall (Tt)
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24.3 The pattern of inheritance
Express Tall Only
? Allele for tall suppresses the expression of
allele for short
? Allele for tall is dominant allele for short
is recessive
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24.3 The pattern of inheritance
X
Parents (pure-breeding)
short
tall
First filial (F1) generation
all tall
self-pollination
Tall Short
3 1
Second filial (F2) generation
277 short
787 tall
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24.3 The pattern of inheritance
F1
G
T
t
T
t
F2
Tt
Tt
tt
TT
TT Tt tt 1 2 1
Genotypic ratio
Tall Short 3 1
Phenotypic ratio
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24.3 The pattern of inheritance
Mendels first law
Of a pair of contrasting characteristics, only
one can be represented in the gametes
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24.3 The pattern of inheritance
The terms used in genetics
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24.3 The pattern of inheritance
The terms used in genetics
alleles
Gene A gene is a short length of DNA on a
chromosome which determines the expression of a
trait.
genes
heterozygous
homozygous recessive
homozygous dominant
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24.3 The pattern of inheritance
The terms used in genetics
alleles
Allele Allele is the alternative forms of a gene.
genes
heterozygous
homozygous recessive
homozygous dominant
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24.3 The pattern of inheritance
The terms used in genetics
alleles
Phenotype Phenotype is the observable
characteristic of an organism, e.g. tall plant or
short plant.
genes
heterozygous
homozygous recessive
homozygous dominant
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24.3 The pattern of inheritance
The terms used in genetics
alleles
Genotype Genotype is the genetic make-up of an
organism, e.g. BB, Bb, or bb.
genes
heterozygous
homozygous recessive
homozygous dominant
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24.3 The pattern of inheritance
The terms used in genetics
alleles
Homozygous Homozygous is the condition in which
an organism has two identical alleles for a
certain characteristic, e.g. tt, Tt.
genes
heterozygous
recessive
dominant
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24.3 The pattern of inheritance
The terms used in genetics
alleles
Heterozygous Heterozygous is the conditions in
which an organism has two different alleles for a
certain characteristic, e.g. Tt.
genes
heterozygous
homozygous recessive
homozygous dominant
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24.3 The pattern of inheritance
The terms used in genetics
Dominant allele A dominant allele e.g. (T) can
express its effect in both homozygous (TT) and
heterozygous (Tt) states. It is usually
represented by a capital letter.
alleles
genes
heterozygous
homozygous recessive
homozygous
dominant
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24.3 The pattern of inheritance
The terms used in genetics
Recessive allele A recessive allele e.g. (t) only
expresses its effect in homozygous state (tt). It
is usually represented by a small letter.
alleles
genes
heterozygous
recessive
homozygous
homozygous dominant
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24.3 The pattern of inheritance
How can you find out the genotype of an organism?
If tall is dominant
How can your determine
the genotype of a tall plant?
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24.3 The pattern of inheritance
Let T be the dominant allele for tall
?
TT
The genotype of the tall plant
or
Tt
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24.3 The pattern of inheritance
Carry out self-pollination
Case I
Case II
P
Tt X Tt
P
TT X TT
G
G
T
t
T
t
T
T
Tt
TT
Tt
tt
TT
F1
F1
tall short 3 1
All are tall
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24.3 The pattern of inheritance
Carry out self-pollination
If all are tall, the unknown tall plant must be
homozygous (TT)
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24.3 The pattern of inheritance
Carry out self-pollination
If a mixture of tall short is obtained in a 31
ratio, then the unknown tall plant must be
heterozygous (Tt)
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24.3 The pattern of inheritance
However, some plants cannot carry out
self-pollination
and most animals cannot carry out self
fertilisation
If black is dominant
How can your determine the genotype of a black
mice?
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24.3 The pattern of inheritance
Let B be the dominant allele for black colour
?
BB
The genotype of the black mice
or
Bb
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24.3 The pattern of inheritance
Carry out a test cross
i.e. cross it with a homozygous recessive
individual
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24.3 The pattern of inheritance
Carry out a test cross
Case I
Case II
P
Bb X bb
P
BB X bb
G
G
B
b
b
B
b
bb
Bb
Bb
F1
F1
All are black
black brown 1 1
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24.3 The pattern of inheritance
Carry out a test cross
If all are black, the unknown black mice
must be homozygous (BB)
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24.3 The pattern of inheritance
Carry out a test cross
If a mixture of black brown is obtained in a
11 ratio, then the unknown black mice must be
heterozygous (Bb)
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24.3 The pattern of inheritance
Summary
How can you find out the genotype of an organism?
dominant characteristic recessive characteristic
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Carry out self- pollination
All offspring show dominant characteristic
Carry out a test cross
dominant characteristic recessive
characteristic 21
All offspring show dominant characteristic
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24.3 The pattern of inheritance
Experiment 24.1 Observation of maize cobs with
grains of different colours

• Your teacher will give you a maize cob with
  grains of two different colours. Examine it
  carefully.
• Count the numbers of dark-coloured grains and
  light-coloured grains.
• Record the results and calculate the ratio of the
  number of dark-coloured to light-coloured grains.
• Deduce the phenotypes and genotypes of the parent
  plants.

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24.3 The pattern of inheritance
How is sex determined in man?
The 23rd pair of chromosome determines sex
Sex chromosomes
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24.3 The pattern of inheritance
How is sex determined in man?
XX
father
mother
XY
ovum
sperms
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50
XY
Girl
XX
Boy
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24.3 The pattern of inheritance
What is pedigree?
A pedigree
is used for the analysis of human inheritance
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24.3 The pattern of inheritance
What is pedigree?
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24.3 The pattern of inheritance
What is pedigree?
Individual 5 crosses with individual 6 to produce
individual 10
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24.3 The pattern of inheritance
What is pedigree?
Individual 3 crosses with individual 7 to produce
two offspring
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24.3 The pattern of inheritance
What is pedigree?
P
F1
F2
There are 3 generations in this pedigree
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24.4 Variations
Variations
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24.4 Variations
What is variations?
Variations are the differences from one another
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24.4 Variations
Examples of continuous variation
Body weight
Heart beat
Hand span
Intelligence quotient
Height
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24.4 Variations
Continuous variation
There is a continuous range of intermediates
between two extremes
Result of interaction of many gene pairs
Influenced by the environment
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24.4 Variations
Continuous variation
A bell-shaped normal distribution curve can be
observed
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24.4 Variations
Examples of Discontinuous variation
Blood group
Eye colour
Sex
Ear lobes
Tongue rolling
Pigmentation
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24.4 Variations
Discontinuous variation
The differences exist two extremes but no
intermediates or the
differences are clear-cut
Result of interaction of small number of gene
Not influenced by the environment
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24.4 Variations
Experiment 24.2 Observation of variation in man

e.g. tongue rolling and the
length of the middle finger A. To study variation
in tongue rolling

• Try to roll your tongue. If you can do this, you
  are a tongue roller. Otherwise you are a
  non-tongue roller.
• Count the number of tongue rollers and non-tongue
  rollers in your class. Record the results.

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24.4 Variations
Experiment 24.2 Observation of variation in man

e.g. tongue rolling and the
length of the middle finger A. To study variation
in tongue rolling

• Measure the length of the middle finger of your
  left hand.
• Divide the finger lengths into suitable
  categories, and record the number in each
  category, like this

length/cm 7.1-7.5
7.6-8.0 8.1-8.5
number 2
4 3
3. Draw a histogram of your results.
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24.4 Variations
Causes of variation
1. Meiosis
2. Random fertilisation
3. Mutation
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24.4 Variations
A. Heredity 1. Meiosis
Since homologous chromosomes separate
independently pass into gametes
OR
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24.4 Variations
A. Heredity 2. Random
fertilisation
Fertilisation of an ovum by a sperm is a random
process
aaBb
AABb
AaBB
Aabb
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24.4 Variations
The suddenly change of the genetic make-up of an
organism
A. Heredity 3. Mutation
Change in a segment of DNA in a chromosome
e.g. polydactyly and sickle cell anaemia
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24.4 Variations
Mutation arise from structural changes in
chromosomes
A. Heredity 3. Mutation
Missing of chromosome e.g. only have 45
chromosomes
Extra chromosome presents
e.g. 47 chromosomes
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24.4 Variations
Mutation may be caused by mutagens
Mutagens
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24.4 Variations
B. Environmental factors
It means that the environmental factors can
modify the phenotype
e.g.
Sunlight
Nutrition
Temperature
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24.4 Variations
B. Environmental factors
A genotypically tall boy may become short
Why?
He is reared with a poor nutrition
e.g. lack of calcium, during
the period of active growth
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24.5 Inherited disorders in humans
Inherited disorders
in humans
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24.5 Inherited disorders in humans
Down syndrome
A normal person
A person with Down syndrome
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24.5 Inherited disorders in humans
Down syndrome
Some degree of learning difficulty
A retarded physical development
Distinctive facial appearance
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24.5 Inherited disorders in humans
Down syndrome
The caused is not yet known
But evidence shows that women aged 30 or older
have a higher chance of giving birth to a child
with Down syndrome
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24.5 Inherited disorders in humans
Colour blindness
is a genetic disorder inherited by a gene on the
sex chromosome called X chromosome
Males are more likely to be
colour blind than females
The most common type is red-green colour
blindness
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24.5 Inherited disorders in humans
G6PD deficiency
Glucose-6-phosphate dehydrogenase deficiency
Inherited by a gene on the X chromosome
People with this deficiency cannot produce an
enzyme called glucose-6-phosphate dehydrogenase
(G6PD)
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24.5 Inherited disorders in humans
Effect of G6PD deficiency
G6PD is an enzyme for protecting red blood cells
against certain poisonous chemicals
Patients red blood cells are destroyed faster
than those produced in the bone marrow
This results in anaemia
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24.4 Genetic engineering
Genetic
engineering
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24.4 Genetic engineering
What is genetic engineering?
It is a technique that
modifies an organisms own genes
OR introduces new genes from another unrelated
organism
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24.4 Genetic engineering
Aim of genetic engineering
Modifying the hereditary properties of organisms
Thus, it causes variations among species by the
human
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24.4 Genetic engineering
Genetic engineering can by applied on
e.g. production of genetically modified foods (GM
foods)
e.g. production of human insulin from bacteria
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24.4 Genetic engineering
Genetically modified foods (GM foods)
With the help of biotechnology
Genes can be transferred from one organism to
another to produce genetically modified organisms
(GMO)
The food produced from GM organisms is called GM
food
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24.4 Genetic engineering
How to make a pest resistant GM plant?
A bacterium produces a toxic protein which kills
caterpillars
The gene coded for the toxin which kills
caterpillars is isolate
The gene for the toxin is introduced into a
bacterium vector
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24.4 Genetic engineering
How to make a pest resistant GM plant?
The vector is transferred into
another bacterium
The bacterium divides repeatedly and the gene in
the vector is replicated
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24.4 Genetic engineering
How to make a pest resistant GM plant?
The vector will be transferred from the bacterial
cells to the plant cells
The plant cells develop to a plantlet
The plantlet develops to a plant which carries
the gene for making the toxin
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24.4 Genetic engineering
Examples of GM foods
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24.4 Genetic engineering
Potential benefits of GM foods
Increasing tolerance to poor environmental
conditions
Providing resistance to pests
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24.4 Genetic engineering
Potential benefits of GM foods
Ordinary tomatoes Expiry date Oct 2003
GM tomatoes Expiry date Oct 2005
Improving nutritional content of crops
Reducing wastage and costs
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24.4 Genetic engineering
Potential benefits of GM foods
Increasing crop yields
GM tomato Ordinary tomato
Eliminating allergy-causing properties in some
foods
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24.4 Genetic engineering
Criticisms against GM foods
Development of super germs
Potential human health impact
Disturbing the balance of ecosystems
Ethical problems
Domination of world market for good products by a
few large countries
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24.4 Genetic engineering
Production of human insulin from bacteria
insulin
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Mind Map
Genetics
is the study of
heredity
examples of genetic diseases
chromosomes
variation
1. Down syndrome
includes
contain
1. continuous variation
2. color blindness
genes
a pair of genes is called
consist of
3. G6PD deficiency
2. discontinuous variation

DNA
the cure methods may be found in
alleles
caused by
Human Genome Project
combinations include
2. environmental factors
1. heredity
human manipulation of genes
homozygous
heterozygous
2 types of expression
includes
genetic engineering
1. meiosis
recessive
dominant
products
2. random fertilisation
factors determine
1. GM foods
3. mutation
phenotype
genotype
2. human insulin
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