LIFE SCIENCES
GRADE 12 REVISION PROGRAMME
TOPIC: PAPER 2
PRESENTER : VEDIKA MAHARAJ
DATE :
15 NOVEMBER 2024
CONTENT WEIGHTINGS PAPER 2
Topic
Weighting %
Marks
DNA: Code of Life 4
18
27
Meiosis
14
21
32
48
36
54
100
150
Term 1:
3
Term 1 and 2
Genetics and
inheritance
Term 3:
2
Evolution
1
TOTAL
RESOURCES
DBE study
guides, SSIP
material
Past papers,
Preparatory
exam papers
Exam guideline
Textbooks
Mind the Gap
Teacher notes
and activities,
one pagers
www.education.gov.za
www.pocketschool.co.za
Learner resources
EVOLUTION
WHAT TO
FOCUS ON
Evolution (54 marks)
Evidence for
evolution
Sources of
variation
Theories of
Lamarck and
Darwin
Punctuated
equilibrium
❖ Fossil record
❖ Biogeography
❖ Modification
by descent
❖ Genetics
❖ Meiosis –
crossing over
and random
arrangement of
chromosomes
❖ Mutations
❖ Random
fertilisation
❖ Random
mating
Lamarck's laws:
❖ Inheritance of
acquired
characteristics
❖ 'Law' of use
and disuse
Punctuated
equilibrium
explains the
speed at which
evolution takes
place
❖ Darwin's theory
of natural
selection
Artificial
selection
Speciation
Human
evolution
Humans select
the characteristic
that they want
animals and
plants to have
Formation of new
species from preexisting species
❖ Similarities
between
humans and
African apes
❖ Differences
between
humans and
African apes
❖ Phylogenetic
trees
❖ 'Out of Africa'
hypothesis
EVIDENCE FOR EVOLUTION
BIOGEOGRAPHY
GENETICS
HOMOLOGOUS STRUCTURES
FOSSIL RECORD
SOURCES OF VARIATION
C – crossing over
R – random
arrangement
R – random
fertilization
R – random
mating
M - mutation
Meiosis
Meiosis
Reproduction
Reproduction
Mutations
CRRRM
TYPES OF VARIATION
Continuous
variation
Characteristics where there is
a range of intermediate
phenotypes
E.g., height, skin colour, hair
colour
Discontinuous
variation
Characteristics that fall into
distinct categories
E.g., blood groups; fingerprints
Two people each gave four descriptions about themselves.
Which ONE of the following combinations are examples of discontinuous
variation?
A. P, Q and S
B. P, R and S
C. Q, R and S
D. P, Q, R and S
THEORIES OF EVOLUTION – LAMARCK
When answering questions based on Lamarck’s theory, remember the following:
•
An inherited characteristic is a characteristic that an offspring is born with,
having been inherited from one of the parents; a characteristic controlled by a gene.
•
An acquired characteristic is a characteristic that an offspring is not born with,
but which develops/is acquired through the course of its lifetime; a characteristic not
controlled by a gene.
Guiding questions when Lamarck’s theory is applied to a new situation:
•
What was the original characteristic?
•
What was the challenge?
•
What did the organism do/what characteristic was then acquired?
•
What was the result?
•
What happened to this acquired characteristic?
•
What was the result of this?
THEORIES OF EVOLUTION – DARWIN
Darwin’s theory of evolution by natural selection:
➢ There is a great deal of variation amongst the offspring
➢ Some have favourable characteristics, and some do not
➢ When there is a change in the environmental conditions
or if there is competition,
➢ Then organisms with characteristics, which make them
more suited, survive
➢ Whilst organisms with unfavourable characteristics,
which make them less suited, die.
➢ The organisms that survive, reproduce
➢ And thus, pass on the allele for the favourable
characteristics to their offspring.
➢ The next generation will therefore have a higher
proportion of individuals with the favourable
characteristic.
Make sure you know the
natural selectin description
in the examination guideline
and be able to apply it to the
question given. Always be
specific!
PUNCTUATED EQUILIBRIUM vs GRADUALISM
GRADUALISM
slow and gradual changes in
species occurring as a result
of a series of small changes.
PUNCTUATED EQUILIBRIUM
rapid change occurs and is
followed by long periods of
no change
SPECIATION
Speciation: is the evolutionary process by which populations
evolve to become distinct species.
Speciation through Geographic isolation:
- If a population of a single species becomes
separated by a geographical barrier (sea, river,
mountain, lake)
- then the population splits into two.
- there is no gene flow between the two populations
- since each population may be exposed to different
environmental conditions/the selection pressure may
be different
- each population undergoes natural selection
independently
- the individuals become genotypically and
phenotypically different
- even if they were to mix, they will not be able to
to interbreed
- the two populations are now different species.
.
MECHANISMS OF REPRODUCTIVE ISOLATION
• Breeding at different times of the year
• Species-specific courtship behaviour
• Plant adaptation to different pollinators
• Infertile offspring
• Prevention of fertilization
EVOLUTION IN PRESENT TIME
Rapidly reproducing species allow us
to study evolution in a short period of
time
Anopheles mosquito
SARS-CoV-2
or novel
coronavirus
HUMAN EVOLUTION
CONTENT
Human evolution
POSSIBLE QUESTIONS
• Interpretation of Phylogenetic trees e.g. Who is the
common ancestor, who is extinct, when did a species on
the diagram originate, how long did they live for, when
did they become extinct etc.)
• Similarities between African apes and humans (What
we share)
• Differences (look at diagrams) skull, bipedalism foramen magnum, spinal cord, pelvis,etc.
• Fossil, genetic and cultural evidence
• Know the fossils that were found in SA as well as the
scientists who found them.
• Out of Africa hypothesis (Exam guideline)
PHYLOGENETIC TREE
Who is the common
ancestor, who is
extinct, when did a
species on the
diagram originate,
how long did they live
for, when did they
become extinct etc.)
DBE MAY-JUNE PAPER 2 2024
1. Identify the type of diagram shown above.
Phylogenetic tree
2. Give the:
(a) Genus that gave rise to the Australopithecus A
Ardipithecus
(b) LETTER that represents the most recent
common ancestor for both H. sapiens and
H. erectus
C
3. Name TWO species that existed at the same time
as H. erectus.
P. troglodytes, G. gorilla, most recent common
ancestor of H. sapiens and H. neanderthalensis
3. Give ONE example of the fossil of Australopithecus
africanus that was found in South Africa.
Mrs Ples, Taung child and Little foot
The diagram below shows the evolutionary
relationship between different species.
SIMILARITIES between Homo sapiens & PRIMATES
11. Sexual dimorphism
10.. Eyes with
cones /colour
vision
9. Two mammary
glands only
1. Large brains/cranium
compared to their body mass
2. Eyes in front/binocular
vision/stereoscopic vision
3. Freely rotating
arms
4. Long upper
arms
5. Elbow joints
allowing rotation of
forearm
8. Upright posture
6. Five fingers, flat nails
instead of claws/bare
fingertips with fingerprints
7. Opposable
thumbs which work
in opposite direction
DIFFERENCES BETWEEN HUMANS AND AFRICAN APES
Humans
African Apes
1. Bipedalism:
Foramen magnum in a forward
position
S-shaped spine
Shorter and wider pelvic girdle
1. Quadrupedalism:
Foramen magnum towards the back of
the skull
C- shaped spine
Longer and narrower pelvic girdle
2. Cranium size: larger
2. Cranium size: smaller
3. Palate shape: semi-circular jaws/Cshaped
3. Palate shape: rectangular jaws/Ushaped
4. Dentition:
No gaps between teeth
Smaller canines
4. Dentition:
Gaps between teeth present(diastema)
Larger canines
5. Non-prognathous
6. Flat face
5. Prognathous
6. Sloping face
7. Cranial ridge absent
8. Brow ridge poorly developed
7. Cranial ridge present
8. Brow ridge well developed
Differences
(study the
diagrams of )
skull, pelvic
girdles, etc.
DBE MAY-JUNE PAPER 2 2024
1. List THREE similarities in relation to vision that are
shared by these organisms.
- Eyes in front
- Binocular vision
- Stereoscopic vision
- colour vision/presence of cones
2. Name ONE species in the diagram that was most
prognathous.
- Gorilla gorilla
3. Describe TWO structures that caused the species
named in question 2 to be most prognathous.
- Large canines/teeth
- Large jaw
The diagrams below represent the skulls of
hominids.
DBE MAY-JUNE PAPER 2 2024
4. Homo naledi was bipedal for most of its adult life.
Explain how the structure of Homo naledi’s skull
would have assisted in bipedalism.
- More forward position of the foramen magnum
- Allows the spine to enter vertically beneath the
skull to support the skull/upright walking
The diagrams below represent the skulls of
hominids.
5. Describe the difference between Homo sapiens and
Gorilla gorilla in relation to the shape of the:
(a) Spine
Homo sapiens has an S-shaped spine
Gorilla gorilla has a C-shaped spine
(b) Pelvis
Homo sapiens has a short and wide pelvis
Gorilla gorilla has a long and narrow pelvis
6. Explain why the Gorilla gorilla species has a cranial ridge
- For the attachment of strong muscles
- to assist in eating tough/hard food
Three lines of Evidence used for a common ancestor of all hominids
Fossil evidence
Genetic evidence
Cultural evidence
FOSSIL EVIDENCE
Species
When it existed
Fossil site
Discovered by
Ardipithecus ramidus
(300 - 350 cm3
5 to 4 mya
Ethiopia
Tim White
A small hominin, weighing about 50 kg; 17 fossils found; an intermediate between apes and
humans
FOSSIL EVIDENCE
Species
When it existed
Fossil site
Discovered by
Australopithecus
afarensis
• Lucy
3.9 to 2.8 mya
Ethiopia
Donald Johansen 1974
2.3 mya
2.5 mya
3.9 to 4.2 mya
Village of Taung (SA)
Sterkfontein caves(SA)
Sterkfontein caves (SA)
Raymond Dart 1924
Robert Broom 1947
Ron Clarke 1995
Near caves in Malapa SA
Brett Eloff & Lee Berger in
2008
Australopithecus
africanus
• Taung child
• Mrs Ples
• Little foot
Australopithecus
sediba -Karabo
1.95 mya
FOSSIL EVIDENCE
Species
When it existed
Fossil site
Discovered by
Homo habilis
2,2 – 1,6 mya
Olduvai, Tanzania
Louis & Mary
Leakey 1960
Homo erectus
2 – 0,4 mya
Java, Indonesia
also in SA and Kenya
Eugene Dubois 1981
Homo naledi
335,000–236,000 ya
Cradle of Human in SA
Lee Burger in 2015
Homo sapiens
0,2 mya to
present
Omo, Ethiopia
Richard Leakey 2005
The genus Homo consists of the one still-living species, Homo
sapiens.
The most significant difference between this genus and
Australopithecus – a much larger brain (about 30% larger).
OUT OF AFRICA HYPOTHESIS
Evidence for the Out of Africa hypothesis:
•
Fossil Evidence: Information on each of the following fossils that serve as
evidence for the Out of Africa hypothesis:
• Ardipithecus (fossils found in Africa only)
• Australopithecus (fossils found in Africa only)
• Homo (Fossils of Homo habilis found in Africa only; oldest fossils of
Homo erectus found in Africa, whilst the younger fossils were found in
other parts of the world)
•
Genetic evidence: Mitochondrial DNA
Analysis of mutations in mtDNA trace oldest female ancestor to East Africa
GENETICS AND INHERITANCE (48 marks)
Mendel’s
laws
Terminology
Sex linked
inheritance
GENETIC AND
INHERITANCE
Monohybrid
crosses
Dihybrid
crosses
Sex
determination
Pedigree
diagrams
WHAT YOU SHOULD FOCUS ON
Monohybrid
cross:
Doing genetic
problems
involving one
characteristic
with 2 alleles
using a
template format
Sex - linked
inheritance:
Doing genetic
problems
involving two
sex -linked
disorders i.e.
haemophilia
and colour
blindness
Pedigree
diagrams/
family tree are
used to study
the inheritance
of
characteristics
in a family over
a number of
generations
Genetic
engineering:
(i) Stem cell
research
(ii) Genetically
modified
organisms
(iii) Cloning
Paternity
testing:
The use of
blood grouping
and DNA
profiles for
paternity testing
Concepts in inheritance:
Understanding the relevant concepts in genetics e.g. genotypes, phenotypes, homozygous,
heterozygous etc.
Mendel’s laws
TERMINOLOGY
Chromatin
vs
Chromosomes
Genes
vs
Alleles
Dominant allele
vs
Recessive allele
Phenotype
vs
Genotype
Homozygous
vs
Heterozygous
Monohybrid
vs
Dihybrid
MENDEL’S LAWS OF INHERITANCE
Exam
Guideline
Pg 11
Exam
Guideline
Pg 12
Exam
Guideline
Pg 12
FORMAT OF A GENETIC CROSS
The visible trait is the phenotype e.g.
tallness, shortness
The genetic make-up of the individual
is it’s genotype e.g. TT or Tt or tt
The alleles segregate (separate)
during meiosis to form gametes
During fertilization the individual gets
one allele from each parent
FORMAT OF A GENETIC CROSS
Remember that by
writing P1 and F1 &
meiosis and
fertilization in the
correct sequence you
can get 2 marks
EMBRYONIC DEVELOPMENT
DOMINANCE
Complete
dominance
One allele is dominant and the other is
recessive, such that the
effect of the recessive allele is masked by
the dominant allele in the
heterozygous condition
Incomplete
dominance
Neither one of the two alleles of a gene is
dominant over the other,
resulting in an intermediate phenotype in
the heterozygous condition
EMBRYONIC DEVELOPMENT
CO-DOMINANCE
Co dominance
Both alleles of a gene are equally dominant
whereby both alleles
express themselves in the phenotype in the
heterozygous condition.
SEX DETERMINATION
Karyotype
Autosomes (1 to 22)
There is a 50%
chance of having a
boy and a 50%
chance of having a
girl
Gonosomes (23)
SEX-LINKED DISORDERS
• Genes located on a sex chromosome are called sex-inked
genes.
• In humans the term usually refers to X-linked characteristics:
genes located only on X chromosomes.
• Fathers can pass X-linked alleles to their daughters, but not sons.
• Mothers can pass sex-linked alleles to both sons and daughters.
• Most of the traits are X-linked, the Y chromosome is so tiny and
does not have genes on it.
• The symbol for an allele is attached to the X chromosome e.g., Xhy
INHERITANCE OF HAEMOPHILIA
✓ The father can only pass the affected
allele to his daughters
✓ The mother can pass the affected
allele to both her sons and daughters
COLOUR BLINDNESS
BLOOD GROUPS
•
•
•
The inheritance of blood groups is an example of multiple alleles
The notation for alleles indicating blood groups is only IA; IB and i
Different combinations of the alleles result in four blood groups
Complete dominance
Complete dominance
Co-dominance
Complete dominance
1-2-3-4 Rule of blood
1. An individual has ONE blood group
2. An individual has TWO alleles for their blood group
3. There are THREE different alleles controlling blood
groups
4. There are FOUR blood groups
DIHYBRID CROSSES
P1
• A genetic cross where two
traits(characteristics) are crossed (two=di)
• Traits are inherited independently
• Mendel’s Law of Independent
Assortment: alleles of a gene for one
characteristic segregate independently of
the alleles of a gene of another
characteristic.
• The genes are on different chromosomes.
GENETIC LINEAGES/PEDIGREES
A genetic
lineage/pedigree traces
the inheritance of
characteristics over
many generations
Non-haemophilic
female
Non-haemophilic
male
Haemophilic female
Haemophilic male
GENETIC LINEAGES/PEDIGREES
Know the meaning of the
symbols and lines used in
pedigree diagrams
STEPS IN SOLVING A PEDIGREE DIAGRAM
➢ Study the key
➢ Look for dominant and recessive characteristics
➢ Fill in the genotype of the individuals with the recessive
condition
➢ Each individual with the recessive condition inherited one
allele from each parent
➢ Work backwards and fill in one recessive allele for each
parent
➢ If the parent has the dominant characteristic fill in a capital
letter as the second letter
➢ Any other individual showing the dominant characteristic is
most likely homozygous dominant – two capital letters
DBE MAY-JUNE PAPER 2 2024
1. How many generations are represented in the diagram? Cystic fibrosis is a genetic disorder caused by a
recessive allele (b).
Three
The pedigree diagram below shows the inheritance
of cystic fibrosis in a certain family.
2. Give the genotype of individual 9.
bb
3. Explain why both individuals 5 and 6 must be
heterozygous for cystic fibrosis.
- Both parents have a dominant and a recessive
allele/Bb
- since they do not have cystic fibrosis
- They have children 8 and 9 with cystic fibrosis/who
are homozygous recessive/bb
- who received one recessive allele from each parent
DBE MAY-JUNE PAPER 2 2024
4. Using the letters B and b, do a genetic cross to show the inheritance of cystic fibrosis when
heterozygou9s parents are crossed.
DNA AND RNA
DNA and RNA:
Structure, location and
functions of DNA and
RNA.
DNA forms genes
which carry hereditary
information.
DNA contains coded
information for protein
synthesis.
RNA plays a role in
protein synthesis.
DNA replication and
its significance:
DNA makes copies of
itself so that it can be
shared between the
resulting daughter
cells during cell
division.
DNA profiling:
Uses and
interpretation of DNA
profiles.
Each person has a
unique DNA profile.
A profile is
represented as an
arrangement of black
bars representing
DNA fragments of a
person.
Protein synthesis:
Process by which
proteins are made in
each cell of an
organism to form
enzymes, hormones
and new structures for
cells.
Process is divided into
(i) transcription
where DNA forms
mRNA. mRNA now
has the coded
message for protein
synthesis
(i) translation where
tRNA reads the code
on mRNA and amino
acids links to form a
protein
POSSIBLE
QUESTIONS
Terminology
Interpretation of
diagrams
Tabulation
Description
Calculation
DNA & RNA
DNA
RNA
sugar
Deoxyribose
Ribose
strand
Double stranded (double
helix)
Single stranded
length
Long
Short
monomer
Nucleotides
Nucleotides
DNA REPLICATION
1. The double helix unwinds.
2. Weak hydrogen bonds between nitrogenous
bases break and two DNA strands unzip
(separate).
3. Each original DNA strand serves as a
template on which its complement is built.
4. Free nucleotides build a DNA strand onto
each of the original two DNA strands by
attaching to their complementary
nitrogenous bases (A to T and C to G).
5. This results in two identical DNA molecules.
Each molecule consists of one original strand
and one new strand.
1
2
3
4
5
PROTEIN SYNTHESIS
Translation (in the ribosomes)
mRNA
Transcription (in the nucleus)
1. The double helix unwinds.
2. Weak hydrogen bonds between nitrogenous
bases break and two DNA strands unzip/separate.
3. One DNA strand acts as the template for the
construction of mRNA in the nucleus.
4. Free RNA nucleotides from the nucleoplasm form
mRNA.
5. mRNA complements the DNA in the nucleus.
6. Coded mRNA leaves the nucleus through the nuclear
pore to the ribose.
7. tRNA pick up amino acids and complement mRNA in
the ribosome.
8. Amino acids bond by peptide bond to form protein.
tRNA
anticodon
DIFFERENCES BETWEEN REPLICATION AND TRANSCRIPTION
DNA REPLICATION
TRANSCRIPTION
Both strands act as templates
One strand acts as a template
Free DNA nucleotides from the nucleoplasm
attach to each strand
Free RNA nucleotides from the nucleoplasm
attach to the template strand
Complementary base pairing occurs
(A-T) and (G-C)
Complementary base pairing occurs
(A-U) and (G-C)
Two Identical DNA molecules are formed
An mRNA molecule is formed
QUESTION (DBE, May-June P2 2023)
1.
Identify organelle 3.
ribosome
2. Describe the role of molecule 1 during this stage of protein synthesis.
- Brings the required/specific amino acid
- according to mRNA/codon to the ribosome
3.
Give the sequence of nitrogenous bases;
(a) At 2
CCU
(b) On the DNA molecule that coded for histidine
GTA
4.
During the synthesis of the same protein, there was a change in the amino
acid sequence because alanine was replaced by trypophan. Explain the
possible reason for this.
- A mutation occurred
- that changed the sequence of nitrogenous bases on DNA from GGG to
GAA
- mRNA codon changed from CCC to CUU
- causing tRNA to bring a different amino acid
The diagram below represents a stage during the synthesis
of a certain protein.
DNA PROFILING
A DNA profile is a pattern of black bars that represents
the DNA fragments of a person.
DNA profiling can be used for the following:
• Paternity testing
• Trace missing persons
• To identify genetic disorders
• To identify criminals in forensic investigations
• To establish family relations
• To match tissues for organ transplants
EMBRYONIC DEVELOPMENT
KEY POINTS TO REMEMBER
• History of the discovery of the DNA molecule (Watson &
Crick, Franklin & Wilkins).
• Structural difference between DNA and RNA.
• The differences between DNA, mRNA and tRNA are
important.
• Differentiate between DNA replication and protein
synthesis.
• Transcription and translation must be learnt by heart.
• DNA profiling is important for application questions.
• Paternity testing involves both parents and the child.
• Uses and interpretation of DNA profiling.
MEIOSIS (21 marks)
It is the type of
cell division
where a diploid
cell undergoes
two cell divisions
to form four
haploid cells
(gametes)
Before meiosis
begins: DNA
replication takes
place. This
results in each
chromosome
consisting of two
chromatids joined
by a centromere
First division:
One diploid cell
gives rise to two
haploid cells
Second division:
The two haploid
cells divides
further to form
four haploid cells
or gametes
Biological
importance:
Crossing over
introduces
genetic variation.
It ensures that
sex cells have a
haploid number of
chromosomes
TERMINOLOGY
•
•
•
•
•
•
•
•
•
•
•
•
Homologous chromosome
Bivalent
Chromosome
Chromatids
Centromere
Centrosome
Crossing over
Chiasma
Karyotype
Non-disjunction
Karyokinesis
Cytokinesis
Question 1.2
INTERPHASE
• DNA replication occurs.
• Each chromosome will now consist of
two chromatids joined by centromere.
• DNA replication helps to double genetic
material to be shared equally during cell
division
Unreplicated chromosome: single
chromosome as it appears in a cell before DNA
replication takes place.
Replicated chromosome: double chromosome
with two chromatids after DNA replication.
Unreplicated
chromosome
Replicated
chromosome
PHASES OF MEIOSIS
What is non-disjunction and what are the consequences of this?
• Spindle fibre fails to separate during meiosis
• Members of one pair of homologous chromosomes fail
to become separated during Anaphase 1 and may
happen in Anaphase 2
• If there is non-disjunction of chromosome pair 21 in
humans, it leads to the formation of an abnormal
gamete with an extra copy of chromosome 21
• 2 gametes receive extra copy of affected chromosome
• 2 gametes lack that chromosome
For Down
Syndrome
focus on extra
copy on
chromosome
21 not less
QUESTION (DBE, May-June P2 2024)
The diagram below represents
metaphase 1 of meiosis.
1. Identify part B.
Cell membrane 
2. State ONE function of part A.
- Produces spindle fibres
3. Explain the contribution of metaphase 1 to natural selection.
- Random arrangement of chromosomes  at the equator
- results in the formation of generically different gametes 
- this leads to increased genetic variation in a population 
- which will cause some individuals to have favourable and
some to have unfavourable characteristics 
- when environmental conditions change 
- those with favourable characteristics will survive 
- and those with unfavourable characteristics will die. 
THINGS TO TAKE TO THE EXAM ROOM
END OF THE PRESENTATION