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DNA and Genetics
Dr André van Wyk
UFS
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Somatic cells
•Cells of the “Soma”= Body cells
•Complete number of chromosomes = 2n
•Diploid
4638
48
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Somatic cells
•Cells of the “Soma”= Body cells
•Complete number of chromosomes =
•Diploid
2n2n
2n
2n
Growth = 2n – 2n
Mitosis
Mitosis:
2n = 2n
or n – n
this correct?
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n
n
n
mitosis
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Sex cells = Half of the chromosome number = n
= haploid cells
Reduction of the chromosome number – a must for the survival of the species
n2n
2n
2n
2n – n
Meiosis
n + n = 2n
Haploid + Haploid = DiploidFERTILISATION
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The importance of Meiosis:
• The process of meiosis reduces the number of chromosomes by half. • Meiosis is the process through which somatic cells (2n) are changed into sex cells (n).• Meiosis ensures that the number of chromosomes in the species stays the same over generations• Meiosis is important to introduce genetic variation.
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http://www.cellsalive.com/cell_cycle.htm
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http://www.cellsalive.com/mitosis.htm
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DNA –Position in the cell
Nucleus
DNA double helix
Chromosomes
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• In each chromosome, the DNA is grouped into "genes." • Your genome contains about 35,000 genes.
In the nucleus of almost every cell in your body is the collection of DNA needed to make you.
DNA in the nucleus is grouped into 23 sets (pairs) of chromosomes that are called your "genome."
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• Instructions is called genetic code• The DNA in your genes tells the cell which amino acids (protein building blocks) must combine to make a protein. It also gives instructions in which sequence the amino acids must combine.
• Thus, DNA provides the blueprint of all life in a living body.• Let us investigate how that this happens.
Instructions to make your whole body and keep it working is contained in DNA
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DNA STRUCTURE
• DNA molecule – double helix (ladder)• String of repeating molecules units called
nucleotides• Each nucleotide consist out of - Deoxyribose sugar - One phosphate group - One nitrogen containing base (A,G,C and T)• Adenine and Guanine – purine bases• Thymine and Cytosine – pyrimidine
bases
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Remember
Did you know : The total length of DNA in mammal cells is 2 metres – in your body 10 billion km
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Structure of DNA
T A
G C
Phosphate
Deoxyribose Sugar
Britannica video
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It's hard to believe that an alphabet with only four letters can make something as wonderful and complex as a person
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DNA Replication
• With cell division -chromosome split in two (mitoses and meiosis )
• DNA must divide • DNA must make exact copies of itself• DNA molecule – unzip• New bases attached themselves in correct place of
each strand• Each strand becomes a double helix• Sometimes mistakes happens – mutation• Mutations is important in evolution
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DNA Replication
Unzip into two single strands
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DNA replication continue
New bases attached themselves in the correct place of each strand
Free nucleotides in nucleoplasm
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Two identical strands are formed
Each strand now becomes a double helix.
Strand 1 Strand 2
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Activity 1
• DNA structure and DNA replication• Group work.
– Instructions
- Use the package marked “DNA” and place the pieces together in order to:
• Know the structure of DNA• Use the pieces and demonstrate the DNA
replication process.
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Significance of DNA replication:
• Important for growth, reproduction • Mutations can cause variation• The main enzyme that catalyze the process is
DNA polymerases • Forms building block for amino acids that forms
proteins• Three bases provides more than the 20
combinations needed to code amino acids (p23)• The sequence of the three bases is called a
codon.
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Activity 2:Extraction of DNA (LO1)
Instructions : Use Worksheet 1
•Step 1
Place ½ teaspoon of ground wheat in a spice jar. Add 10 teaspoons of tap water to the ground wheat and mix non-stop with a wooden stick for 3 minutes
•Step 2
Add ¼ teaspoon of dishwashing liquid to the cells that have been suspended in water in step 1. Mix gently with a wooden stick every ½ minutes for 5 minutes.
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Step 3• Remove all foam that may have formed on top
of the mixture with a paper towel.
Step 4• Tilt the jar and slowly add an estimated equal
volume of methylated spirit to the mixture and carefully pouring it down the side of the jar.
Step 5• Use the wooden sticks to fish these “white slimy
threads” out of the spice jar and transfer it to a 10ml pill vial.
Rubric
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Assessment of DNA
• Draw and label a diagram of DNA (LO1:AS2)
(manipulate data)
• Make a model of DNA – (LO1:AS3)
( Communicate data/findings)
• Extraction of DNA out of wheat (LO1:AS2)• http://rubistar.4teachers.org (example rubric 1)
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1. Identify the above molecule.2. Give labels for parts numbered 1to 53. Describe how the above molecule replicates itself.4. Why is it of significance that this molecule can replicate itself?
Questions on the DNA Molecule
1
2
3
4
5
G
T
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• Diabetics need insulin to live
• Diabetes use insulin from pigs and cattle. This is not the same as human insulin and sometimes produces side effects. With genetic engineering, bacteria are used to produce some human insulin
Bacterial DNA - Manufacturing of insulin
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1. A string of DNA is taken from a bacterium
2. A piece is cut out using enzymes as ‘chemical scissors’
3. A cell is taken from a human pancreas. The gene for insulin is cut from the chromosome
4. The insulin gene is put into the string of bacteria DNA
5. The bacteria reproduce, making
clones of themselves
6. The insulin is collected and purified ready for use
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Structure of RNA
• Single strand
• Sugar is ribose
• Four nitrogen bases
Adenine and Uracil
Guanine and Cytosine
U
G
C
A
Assessment : Make a stick drawing of RNA
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Assessment:Tabulate the Differences between DNA and RNA
DNA RNADouble strand Single strand
Deoxyribose sugar Ribose sugar
Thymine and Adenine Thymine and Uracil
Nucleoplasm Nucleoplasm and cytoplasm
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Three types of RNA and their functions
1. Messenger RNA (mRNA) which acts as a template for protein synthesis and has the same sequence of bases as the DNA strand that has the gene sequence.
1. Messenger RNA (mRNA)2. Transfer RNA (tRNA)3. Ribosomal RNA (rRNA)
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2. Transfer RNA (tRNA), one for each triplet codon that codes for a pecific amino-acid (the building blocks of proteins). tRNA molecules are covalently attached to the corresponding amino-acid at one end, and at the other end they have a triplet sequence (called the anti-codon) that is complementary to the triplet codon on the mRNA.
3. Ribosomal RNA (rRNA) which make up an integral part of the ribosome, the protein synthesis machinery in the cell.
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RNA Transcription
• DNA is the template
• DNA manufactures mRNA in nucleus
• Transported out from the DNA of nucleus
into the cytoplasm
• Transcription similar to DNA replication
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U
G
C
A
G
U
C
A
mRNA structureRNA bases pairing
TRANSCRIPTION
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Crystal structure of tRNA molecules.
AnticodonC C G
G G C
tRNA
mRNA`
CodonmRNA
The single-stranded chain is folded in a 'clover-leaf’
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DNA unzip to expose a gene
mRNA copies the gene
mRNA moves to ribosome r RNA
tRNA carries amino acid to ribosome
Amino acids linked up to form protein molecule
The process of translation and protein synthesis
TRANSLATIONTRANSCRIPTION
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Protein synthesis in the cell
Free amino acids
tRNA brings amino acid to ribosome
Ribosome incorporating amino acid in protein chain
mRNA being translated
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Assessment of RNA (LO2)1. Describe the role of DNA and RNA in the following
1.1 Formation of mRNA by transcription
1.2 Movement of mRNA from the nucleus to cytoplasm
1.3 Translation of mRNA (codon) to form protein using tRNA (anticodon)
2. Determine the sequence of bases in mRNA from DNA molecule.
GTA ATG TGG TTT
3. Give the mRNA sequence that matched the anticodons of the tRNA
PROLINE
G C U
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Activity 2
• Transcription and translation.
• Group work.– Instructions
- Use the package marked “Protein synthesis” and imitate the processes of transcription and translation with the pieces in the pack.
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Protein synthesis (assessment)
2
5
3
6
1.
4
7
1. Give labels for number 1 to 7
2. Describe the processes that occur at numbers 2,3,5
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Part 2 Chromosomes, meiosis and
sex cells
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Mitoses
• Revision:• Group work: • Using the clay provided and build a model
of the process of mitoses. The clay must represent the chromosomes.
• Cut pieces of paper to represents the cell structures/stages.
• Especially pay attention to the structure of the chromosomes.
Mitoses
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Meiosis
First meiotic division
Prophase 1
Anaphase 1:
Metaphase 1
Two daughter cells
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Meiosis IInterphase: Duplication of each chromosome
Prophase I: Paring of homologous Chromosomes - chiasmata – crossing over
Metaphase I: Organisation of two tetrads in the equatorial plane
Anaphase I: Separation of homologous chromosomes
Completion of Meiotic division:Two daughter cells each with two dyads
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Crossing over
Significance of crossing over:
Genetic material is exchanged – cause variation
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Second meiotic division
Metaphase II
Anaphase II
Four haploid cells, each with two chromosomes known as reproductive cells. (ovum or sperm)
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Metaphase II: Each daughter cell from the previous division has two dyads
Second meiotic division
Anaphase II:–Mitotic separation of chromatids of each chromosome
Completion of second meiotic division – four haploid cells, each with two chromosomes known as reproductive cells. (ovum or sperm)
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Sex cells
Sperm and Ovum
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Activity 3 (LO1)
Each group use the clay and build the process of meiosis
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The importance of Meiosis:
• The process of meiosis reduces the number of chromosomes by half• One cell divides into four cells with each the haploid (n) number of chromosomes• The first meiotic division reduces the number of chromosomes• The second meiotic division is actually mitosis which increases the number of cells• Meiosis is the process through which gametes are prepared for fertilisation.• Meiosis ensures that the number of chromosomes in the species stays the same over generations• Meiosis is important to introduce genetic variation.
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Assessment
• Use diagrams to identify the different phases • Use one word to describe the paired
chromosomes• What would the chromosome number in each
cell be at the end of meiosis? • Describe the importance of crossing over• Describe the importance of meiosis• Explain why the four cells at the end of meiosis
is not identical
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Chromosomes
(p43)
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Chromosomes
Homologous pair
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Karyogram and karyotype
• Diagram of arrangement of chromosomes
• Chromosomes are paired according to size
• Arrangement is called karyogram
• Set of chromosomes is called a karyotype
• Human karyogram shows the 23 pairs of chromosomes
• Chromosome set 23 indicate the sex of the individual
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Karyogram
Normal Male Normal Female
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Down syndrome• Down's syndrome is caused by the presence of three copies of the 21st chromosome.• This chromosomal defect is known as Trisomy-21.• Down's syndrome almost always results in mental retardation, though the severity of the retardation varies.
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Characteristics of Down syndrome
Small, oblique eyes
Flattened, nasal bridge
Open mouth Protruding tongue Broad neck
Small underdeveloped ears set low on head
Epicanthic fold
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Incurved finger
Single palmar (“simian”) crease
Short broad hands
Wide gap between first and second toe
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Assessment
• Identify on the karyogram if the individual is female or male?
• Does this individual has an abnormal number of chromosomes?
• Name the genetic disease that the individual suffer from.
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Assessment (LO1)Use the table below and draw a graph to show the relation of maternal age to Down syndrome
Relation of Maternal Age to Down Syndrome
Mother’s age (Years)
Risk of Occurrence
20 - 29 1 in 2 000
30 - 34 1 in 750
40 - 44 1 in 100
45 - 49 1 in 40
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This is a rare condition of premature ageing that begins in childhood or early adult life and leads to death within a few years
Hutchinson-Gilford progeria syndrome
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Albinism
A person or animal whose melanocytes in the skin do not contain any melanin (pigment) is called an albino. This results in a characteristic appearance with snow-white hair, pink or blue eyes, and pinkish-white skin that is very sensitive to sunlight
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♂Carrier A a
♀Carrier A a
½ A ½ a ½ A ½ a
¼ AA ¼ Aa ¼ aA ¼ aa
carriers ½
normal phenotype ¾
albino
Albinism is inherited
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Part 3Genetics
Genetics is the scientific study of how physical, biochemical, and behavioural traits are transmitted from parents to their offspring
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Terminology• Genes - small portions of DNA and protein• Alleles - genes controlling same characteristic example eye
colour• Haploid – half the number of chromosomes• Diploid – full set of chromosomes• Somatic/body cells (containing genes in pairs)• Sex cells/gametes (containing unpaired genes)• Homozygous – has similar genes for specific characteristic• Heterozygous- unlike genes for a specific characteristic• Human genome - the entire genetic blueprint of a human
beings
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Father of Genetics
Gregor Mendeldeveloped the principles of heredity while studying seven pairs of inherited characteristics in pea plants. Although the significance of his work was not recognized during his lifetime, it has become the basis for the present-day field of genetics.
Father of Genetics
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Mendel – Monohybrid crosses
Stamen -male
Carpel female
Smooth or dented seeds
Green or yellow seeds
Green or yellow pods
White or purple flowers
P1
F1
Parents
Generation 1
YY yy
Yy Yyx
Generation 2
F2
Punnet square
Yy
YY Yy
yy
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Father of GeneticsGenetics: Assessment
Female
Male
Punnet Y Y
y Yy Yy
y Yy Yy
Question: Determines the Genotype and the Phenotype, by means of a Punnet diagramme, the F1 and F2 generations when a homozygote yellow coloured plant (Dominant - Y) is crossed with a white one Resssive - y).
male female
P1 zygotes: YY x yy
Meiosis
Gametes: Y Y y y
Fertilisation:
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F1: Genotype = Heterozygous 100% Yy
Phenotype = 100% Yellow
F2 generation: male female
female
male
Punnet Y y
Y YY Yy
y Yy yy
P2 zygotes: Yy x Yy
Meiosis
Gametes: Y y Y y
Fertilisation:
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F2: Genotype = Homozygous 25% YY
Heterozygous 50% Yy
Homozygous 25% yy
Phenotype = 75% Yellow
25% White
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Assessment (LO1)100%
50%
25%
B100%
50%
25%
A 100%
50%
25%
C
Bb bb Bb bb BB
The following histograms represent the percentage of various genotypes that occur in the F1 generation in several monohybrid crosses. For each, predict the genotypes of the parents (P1).
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Inheritance and variation
Father
Off spring
Mother
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Human traits
Lobed ears
Dark wavy hair
Brown eyes
Straight nose
Projecting chin
Dominant traits
Blue eyes
Blond straight hair
Upturned nose
Receding chin
Unlobed ears
Recessive traits
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Inherited traitsBent little finger
Widow’s peak
Dimples
Rolled tongue
Earlobes: Free and Attached
Hitch-hiker’s thumb Mid-digit hair
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Activity 4
• Complete the tabel on human traits in your group
• Study the project handed out to you
• Discuss in your group how this project covers LO1, LO2 and LO3 (SAG)
• How can this project help you with assessment.
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Sex determination
XX = girl XY = boy
Is it a boy or a girl?
Hallo here am I
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Blood types
• The method of classifying human blood on the basis of the inherited properties of red blood cells (erythrocytes) as determined by their possession or lack of the so-called antigens A and B.
• Thus, persons may have type A, type B, type O, or type AB blood. The A, B, and O blood groups were first identified by the Austrian immunologist Karl Landsteiner in 1901.
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Blood – multiple alleles
• Four phenotypes A,B,AB and O• Are determined by presence of two out of three
possible alleles namely A,B and O
Phenotype Possible genotype
A AA, AO
B BB, BO
AB AB
O OO
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Assessment
In the TV series Days of Our Lives, two good friends, namely, Hope and Lexie each gave birth to a son. These babies were deliberately switched in the hospital. From the following blood types, determine which baby belongs to which parents:
Baby 1 : Type OBaby 2 : Type A
Hope : Type BHope’s Husband : Type AB
Lexie : Type BLexie’s Husband : Type B
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Human Pedigrees (p73)
Shows the line of ancestors: the line of ancestors of an individual animal or person.
• Used to trace diseases like Haemophilia, Muscular dystrophy, Cystic fibrosis
Haemophilia
Affected male
Female carrier
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•Discuss whether insurance companies should have the right to refuse cover for a child if prenatal tests results indicate that the child will suffer a severe genetic disorder?
•Using the technology available today, suppose that you could learn with certainty, that by the age of 60 you would suffer from a genetic disease. Would you like to know?
• Makae and Sipho want to marry. Show, in a family tree form, all the possible genotypes of a child they intend to have. (Gg xGg) gg = cystic fibrosis.
Assessment of LO 3 – Ethical dilemmas
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Genetic counseling
• Genetic counseling, a process where information and advice is given about inherited disorders. Often it is given to a couple who are planning to have a child but who suspect that there is a greater than normal risk of the child being affected by a genetic disorder
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Genetic modification
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•In genetic modification, scientists use restriction enzymes to isolate a segment of DNA that contains a particular gene of interest (1).
•In this instance, it is a human gene. A plasmid extracted from its bacteria and treated with the same restriction enzyme can hybridize with this fragment’s “sticky” ends of complementary DNA (2).
•The hybrid plasmid is reincorporated into the bacterial cell, where it replicates as part of the cell’s DNA (3).
• A large number of daughter cells can be cultured and studied, and their gene products may be extracted for further use (4).
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Examples of Genetic modification
A scorpion venom gene, engineered into a virus, is used as a spray to kill insects
Poultry with modified genes are resistant to salmonella food poisoning bacteria, and lay bigger eggs more often
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Genetically modified pigs grow faster, have less fat, and produced cholesterol-free meat
Salmon eggs have genes inserted into them which make them grow ten times faster than normal
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Assessment (LO3)
These tomatoes have been given genes from fish which make them frost resistant and fresh for longer. Would you eat them?
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Do a survey on the following two questions:
Do people know what genetic modified foods are?
Will they eat genetically modified food?
Design a questionnaire
Use two groups of people
• Group 1: 15 - 30
• Group 2: 30 – 50 years old
Draw bar graph on the results obtained in the two questions – plot both sets of data on the same graph
Draw a Pie chart with the results
Write down a hypothesis for your investigation
Write down your independent and dependant factors
Write down your conclusion for this investigation
LO1 assessment
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Extinct zebra
Tracy
Etienne
Interbreeding
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• Baby of the thought extinct zebra is in the Cape museum since 1858 – stuffed by taxidermist
• Later Mr Rau curator of the museum decided to send it to be re-stuffed
• They discovered some muscle tissue left on the inside of the skin
• DNA testing show this zebra is related to Equus burchelli (still alive today)
• Special inbreeding programme was started and today we have back the original species
The story of the extinct zebra