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DNA and Genetics
Dr André van Wyk
UFS
38
46
Somatic cells
48
•Cells of the “Soma”= Body cells
•Complete number of chromosomes = 2n
•Diploid
2n
2n
2n
Growth = 2n – 2n
Mitosis
2n
Somatic cells
•Cells of the “Soma”= Body cells
•Complete number of chromosomes =
•Diploid
Mitosis:
2n = 2n
or n – n
this correct?
n
n
mitosis
n
2n
n
2n
2n – n
Meiosis
2n
Sex cells = Half of the chromosome number = n
= haploid cells
Reduction of the chromosome number – a must
for the survival of the species
n + n = 2n
Haploid + Haploid = Diploid
FERTILISATION
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.
http://www.cellsalive.com/cell_cycle.htm
http://www.cellsalive.com/mitosis.htm
DNA –Position in the cell
DNA double helix
Nucleus
Chromosomes
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."
• In each chromosome, the DNA is grouped into
"genes."
• Your genome contains about 35,000 genes.
Instructions to make your whole body and
keep it working is contained in DNA
• 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.
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
Remember
Did you know :
The total length of DNA
in mammal cells is 2
metres – in your body 10
billion km
Structure of DNA
T
A
G
C
Phosphate
Deoxyribose
Sugar
Britannica video
It's hard to
believe that an
alphabet with
only four letters
can make
something as
wonderful and
complex as a
person
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
DNA Replication
Unzip
into two
single
strands
DNA replication
continue
New bases
attached
themselves
in the
correct
place of
each strand
Free nucleotides
in nucleoplasm
Two identical strands are formed
Each strand now becomes a double helix.
Strand 1
Strand 2
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.
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.
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.
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
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)
Questions on the DNA Molecule
1
G
3
2
T
4
5
1. Identify the above molecule.
2. Give labels for parts numbered 1to 5
3. Describe how the above molecule
replicates itself.
4. Why is it of significance that this molecule can
replicate itself?
Bacterial DNA - Manufacturing of insulin
• 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
1. A string of DNA is taken from a bacterium
6. The insulin is
collected and purified
ready for use
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
5. The bacteria
reproduce, making
clones of themselves
4. The insulin gene
is put into the string
of bacteria DNA
Structure of RNA
• Single strand
U
G
A
• Sugar is ribose
• Four nitrogen bases
Adenine and Uracil
Guanine and Cytosine
C
Assessment : Make a stick drawing of RNA
Assessment:
Tabulate the Differences between DNA and RNA
DNA
RNA
Double strand
Single strand
Deoxyribose sugar
Ribose sugar
Thymine and Adenine
Thymine and Uracil
Nucleoplasm
Nucleoplasm and
cytoplasm
Three types of RNA and their
functions
1. Messenger RNA (mRNA)
2. Transfer RNA (tRNA)
3. Ribosomal RNA (rRNA)
 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.
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.
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
RNA bases pairing
U
A
G
C
A
U
C
G
mRNA structure
TRANSCRIPTION
Crystal structure of tRNA
molecules.
tRNA
C C G Anticodon
GGC
Codon
mRNA
The single-stranded chain is
folded in a 'clover-leaf’
mRNA`
The process of translation and protein synthesis
TRANSLATION
TRANSCRIPTION
mRNA moves to
ribosome r RNA
tRNA carries
DNA
unzip to
expose a
gene
mRNA copies
the gene
amino acid to
ribosome
Amino acids
linked up to
form protein
molecule
Protein synthesis in the cell
Free amino acids
tRNA brings amino
acid to ribosome
mRNA being
translated
Ribosome
incorporating
amino acid in
protein chain
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
GCU
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.
Protein synthesis (assessment)
1.
2
3
4
6
5
7
1. Give labels for number 1 to 7
2. Describe the processes that occur at
numbers 2,3,5
Part 2
Chromosomes, meiosis and
sex cells
Mitoses
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.
Meiosis
First meiotic division
Prophase 1
Metaphase 1
Anaphase 1:
Two daughter cells
Meiosis I
Interphase: 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
Crossing over
Significance of crossing over:
Genetic material is exchanged – cause variation
Second meiotic division
Metaphase II
Anaphase II
Four haploid cells, each with two chromosomes known as reproductive
cells. (ovum or sperm)
Second meiotic division
Metaphase II: Each daughter cell from the
previous division has two dyads
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)
Sex cells
Sperm and Ovum
Activity 3 (LO1)
Each group use the clay and build the process
of meiosis
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.
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
Chromosomes
(p43)
Chromosomes
Homologous pair
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
Karyogram
Normal Male
Normal Female
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.
Characteristics of Down syndrome
Epicanthic fold
Small, oblique eyes
Flattened, nasal bridge
Open mouth
Protruding tongue
Broad neck
Small
underdeveloped
ears set low on
head
Wide gap between
first and second toe
Incurved
finger
Single palmar
(“simian”) crease
Short broad
hands
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.
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
Risk of Occurrence
Mother’s age
(Years)
20 - 29
1 in 2 000
30 - 34
1 in 750
40 - 44
1 in 100
45 - 49
1 in 40
Hutchinson-Gilford progeria syndrome
This is a rare condition of premature ageing that
begins in childhood or early adult life and leads
to death within a few years
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
♂Carrier
Aa
Albinism is
inherited
½A
¼ AA
♀Carrier
Aa
½a
¼ Aa
½A
¼ aA
carriers ½
normal phenotype ¾
½a
¼ aa
albino
Part 3
Genetics
Genetics is the scientific study of how
physical, biochemical, and behavioural
traits are transmitted from parents to
their offspring
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
Father of Genetics
Gregor Mendel
developed 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.
Mendel – Monohybrid crosses
Stamen -male
Parents
Carpel
female
YY
yy
P1
Generation 1
Smooth or
dented seeds
F1
x
Yy
Yy
Generation 2
Green or
yellow
seeds
F2
Green or yellow pods
YY
Yy
Yy
yy
Punnet square
White or purple flowers
Genetics:
Assessment
Father of Genetics
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
P1 zygotes:
female
YY
x
yy
Y
Y
y
Meiosis
Gametes:
y
Fertilisation:
Female
Male
Punnet
Y
Y
y
Yy
Yy
y
Yy
Yy
F1:
Genotype = Heterozygous 100% Yy
Phenotype = 100% Yellow
F2 generation:
P2 zygotes:
male
female
Yy
x
Yy
Y
y
Y
Meiosis
Gametes:
y
Fertilisation:
male
female
Punnet
Y
y
Y
YY
Yy
y
Yy
yy
F2: Genotype = Homozygous 25% YY
Heterozygous 50% Yy
Homozygous 25% yy
Phenotype = 75% Yellow
25% White
Assessment (LO1)
100%
A
100%
B
100%
50%
50%
50%
25%
25%
25%
Bb
bb
Bb
C
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).
Inheritance and variation
Father
Off spring
Mother
Human traits
Recessive traits
Dominant traits
Dark
wavy
hair
Brown
eyes
Straight
nose
Projecting
chin
Blond
straight
hair
Blue
eyes
Upturned
nose
Receding
chin
Unlobed ears
Lobed ears
Inherited traits
Hitch-hiker’s thumb
Widow’s peak
Mid-digit hair
Bent little finger
Earlobes: Free and Attached
Dimples
Rolled tongue
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.
Sex determination
Is it a boy or a girl?
XX = girl
Hallo here
am I
XY = boy
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.
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
B
AB
O
AA, AO
BB, BO
AB
OO
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 O
Baby 2
:
Type A
Hope
:
Type B
Hope’s Husband
:
Type AB
Lexie
:
Type B
Lexie’s Husband
:
Type B
Human Pedigrees (p73)
Shows the line of ancestors: the line of
ancestors of an individual animal or person.
Haemophilia
Affected
male
Female
carrier
• Used to trace diseases like Haemophilia, Muscular
dystrophy, Cystic fibrosis
Assessment of LO 3 – Ethical dilemmas
•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.
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
Genetic modification
•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).
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
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
Assessment (LO3)
These tomatoes have been given genes from fish
which make them frost resistant and fresh for
longer. Would you eat them?
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
LO1
assessment
• 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
Extinct zebra
Etienne
Tracy
Interbreeding
The story of the extinct zebra
• 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
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