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    BEHAVIOUR OF CHROMOSOMES

 DURINGTHE DIFFERENT PHASES OF

 MEIOSIS I

–  During
prophaseP I 

–  chromosomes
pairPup/homologous pairs /bivalents
form 

–  Crossing
overPexchange of genetic material
occurs 

–  between
chromatidsP/adjacent chromosome pairs 

–  During
metaphaseP I of meiosis 

–  homologous
chromosomesP/chromosome pairs are arranged 

–  at the equatorPof the cell 

–  in a
randomP way 

–  with
the chromosome attached to the spindle fibreP 

–  During
anaphase P I 

–  chromosome
pairs separateP/chromosomes move to
opposite poles 

–  During
telophase P I 

–  the
chromosomes reach the poles of the cellP 

EVENTS THAT LEAD TO DOWN SYNDROME

–  Non-disjunction
occurredP/A homologous pair of
chromosomes 

–  at
position 21P 

–  failed
to separateP 

–  during
anaphaseP 

–  resulting
in one gamete with 24 chromosomesP
/ an extra chromosome /    chromosomes at
position 21 

–  The
fertilisation of this gamete with a normal gameteP/gamete    with 23 chromosomes /1 chromosome at
position 21 

–  results
in a zygote with 47 chromosomesP 

–  There
are 3 chromosomesP/an extra chromosome
at position 21/ this is Trisomy 21 HOW
MEIOSIS CONTRIBUTES TO GENETIC VARIATION 

 Crossing
overP 

–  Occurs
during prophase IP 

–  Chromatids
of homologous chromosomes overlapP 

–  at
points called chiasmaP/ chiasmata 

–  Genetic
material is exchangedP 

–  resulting
in new combinations of genetic material Pfrom
both parents 

 Random
arrangement of chromosomes 

–  Occurs
during metaphase I P/ II 

–  Each
pair of homologous chromosomes P
/each chromosome 

–  may
line up in different waysP on the equator of
the spindle 

–  allowing
the gametes to have different combinations of maternal and paternal    chromosomes P 

–  so
that they separate in a randomP/
independent manner 

–  resulting
in new combinations of genetic materialP

HOW
MUTATIONS CONTRIBUTE TO GENETIC VARIATION  

Two types of mutations:  
gene mutation and


chromosome mutations

–  A geneP
mutation occurs 

–  as a
result of a change in sequence of nitrogenous basesP
in the DNA molecule 

– A chromosomePmutation occurs as a 

–  result
of a change in the structure of a chromosomePOR

–  a
change in the number of chromosomes during meiosisP 

– Mutations
that occur in sex cellsP 

–  are
passed on to the new generationsP 

–  creating
new characteristicsP 

DNA: CODE OF LIFE &
PROTEIN SYNTHESIS 

THE LOCATION, STRUCTURE AND FUNCTIONS OF A DNA
MOLECULE  

–  The
DNA is located in the nucleusP/chromosome/genes/mitochondria 

–  DNA
is a nucleic acidP 

–  It
is double strandedP molecule

–  and
arranged in the form of a helixP 

–  consisting
of building blocks called nucleotidesP    The three components of a nucleotide are as
follows: 

–  Nitrogenous
basesP 

–  Phosphate
portionP 

–  Deoxyribose
sugar portionP (in DNA) 

–  4
nitrogenous bases Pare A,T,C,GP  

–  adenine
(A) binds with thymine (T) P and cytosine (C)
binds with guanine (G)P 

–  by
weak hydrogen bondsP 

–  Sections
of DNA carry hereditaryPinformation 

–  DNA
contains coded information for protein synthesisP 

STRUCTURAL
DIFFERENCES BETWEEN DNA AND RNA.  

DNA REPLICATION

–  The
DNA- double helix molecule unwindsP
within the nucleus 

–  WeakP hydrogen bonds between the two
strands breakP/ the molecule
unzips 

–  Each
strand serves as a templateP to form a new strand

–  Free
DNA nucleotidesP attach to the
individual strands 

–  with
complementary nitrogenous basesP
pairing/ (A to T and C to G) 

–  Two
genetically identical DNA moleculesP
are formed 

–  Process
is controlled by enzymesP

EXTRACTING DNA (practical work)

•             
Grating the onion, increases the surface area
for the dishwashing liquid, salt and    
tenderizer to act on. 

•             
Placing the beaker in hot water allows for the
cell breakdown to occur faster  TRANSCRIPTION IN PROTEIN SYNTHESIS

–  Occurs
within the nucleusP 

–  Double-stranded
DNA unwindsP 

–  and
unzipsP/2 DNA strands separate/the weak
hydrogen bonds break

–  One
strand is used as a templateP 

–  to
form mRNAP 

–  using
free RNA nucleotides from the nucleoplasmP 

–  The
mRNA is complementary to the DNAP/
A-U, C-G 

–  This
process is controlled by enzymesP 

–  The
coded message for protein synthesis is thus copied onto mRNAP 

–  Each
base triplet is called a codonP 

TRANSLATION IN PROTEIN SYNTHESIS

–  mRNA
moves from the nucleusP/to the ribosome
within the cytoplasm 

–  The
anticodon on the tRNA matches the codon on the mRNAP 

–  tRNA
brings the required amino acidP 

–  to
the ribosomeP 

–  Amino
acids are joined by peptide bondsP 

–  to
form the required proteinP/ polypeptide chain.

HOW A GENE MUTATION INFLUENCES THE STRUCTURE OF
A PROTEIN

–  A
mutation is a change in the nucleotide/nitrogenous base sequenceP 

–  of a
DNA moleculeP/a gene 

–  since
mRNA is copied from the DNA moleculeP 

–  during
transcriptionP 

–  This
will result in a change in the codonsP 

–  As a
result, different tRNAP molecules 

–  carrying
different amino acidsP will be
required 

–  The
sequence of amino acids changesP 

–  resulting
in the formation of a different proteinP 

–  If
the same amino acid P is coded for 

–  there
will be no changeP in the protein
structure 

USES OF DNA PROFILING / ANALYSIS  

–  To
investigate crimes P/ resolve
disputes 

–  To
identify organisms from their remainsP 

–  To
identify family relationships other than paternityP
e.g. siblings or cousins 

–  To
test for the presence of specific allelesP
/ genes that cause a genetic disorder – To establish matching tissues for organ
transplantsP 

GENETICS 

MENDEL’S LAW OF DOMINANCE

–  When
two organisms with pure breedingP
contrasting characteristics Pare crossed 

–  All
the individuals of the F₁ generation will display the dominant traitP 

  OR 

–  If
an organism is heterozygousP the 

–  dominant
alleleP will 

–  determine
the phenotypeP

MENDEL’S LAW OF INDEPENDENT ASSORTMENT  

–  The
various genes are separateP entities and do not
influence each other in any way 

–  They
sort themselves out independentlyP 

–  during
gamete formationP 

–  since
homologous chromosomes arrange themselves randomlyP
along the equator 

–  during
metaphase IP 

MENDEL’S LAW OF SEGREGATION

–  Each
characteristic is controlled by two genes situated on homologous chromosomesP 

–  During
meiosisP /anaphase/ when gametes form, 

–  the
two genes are separated or segregatedP 

–  enabling
a gamete to contain one of the two allelesP
from each parent

SUMMARY OF GENETIC CROSSES 

WHY THE SEX OF A CHILD IS DETERMINED BY THE MALE
GAMETE

–  Normal
males have one X and one YP 

–  Normal
females have two XP chromosomes 

–  The
female always provides the X- chromosome in the ovumP 

–  If
an ovum is fertilized by an X bearing spermP    a female/girlP
is formed 

–  If
an ovum is fertilized by a Y bearing spermP 

–  a
male/boyP is formed 

WHY ARE THERE MORE MALES THAN FEMALES WITH
COLOUR-BLINDNESS  

–  Males
only have one X-chromosomeP 

–  If
this chromosome carries the recessive alleleP/X^b 

–  the
male will be colour-blindP 

–  the
Y-chromosome in males, does not carry any allele to mask the effect of the
colour-   blind alleleP 

–  Females
have 2 X-chromosomesP 

–  They
need to have two recessive allelesP/X^b
X^b to be affected 

–  A
dominant allele on the other X-chromosome will mask the effectP of the recessive    trait. 

A HAEMOPHILIAC FEMALE MARRIES A MALE WITHOUT
HAEMOPHILIA EXPLAIN WHY ALL THEIR SONS WILL BE HAEMOPHILIAC

–  An
individual inherits one allele from each parentP 

–  The
Y chromosome was inherited from the fatherP 

–  and
the recessive allele / X^h was inherited from the motherP 

–  since
the mother has two recessive allelesP/X^h
X^h 

–  A
son only needs to get one recessive allele to be haemophiliacP since the 

–  Y-chromosome
does not carry any allele to mask the effect of haemophilia alleleP

WHY FEMALES HAVE A SMALLER CHANCE OF SUFFERING
FROM HAEMOPHILIA  

–  Haemophilia
is caused by a recessive alleleP 

–  Carried
on the X chromosomeP 

–  Females
have two X chromosomesP/ Males only have one
X chromosome 

–  Females
must inherit two copies of the recessive alleleP 

  females who
inherit only one of the recessive alleles are still non-haemophiliacP 

GENETIC MODIFICATION

–  Removing
a useful gene from one organismP
and 

–  inserting
it into another organismP

–  to
produce beneficial characteristicsP

ADVANTAGES OF GENETIC ENGINEERING  

–  Production
of medicationP/ resources
cheaply 

–  Control
pests with specific genes inserted into a cropP 

–  Using
specific genes to increases crop yieldsP
/ food security  – Selecting genes to
increase shelf-life of plant productsP 

WHY SOME PEOPLE MAY BE AGAINST THE USE OF
GENETIC ENGINEERING

–  The
long-term effects on health are unknownP
which 

–  could
lead to health problems in the futureP 

–  The
long-term effects on biodiversityP/
damaging ecosystems/nature 

–  People
are morally opposedP as 

–  humans
are interfering with natureP/playing
God/interfering with the rights of every   
species 

–  Initially
it is an expensive processP and 

–  many
people/countries may not afford it /research money could be used for other
needs  CLONING  

–  A
somatic diploid cell from tissue is usedP  – The nucleus is removed from this cellP – and is placed inside an “empty”
ovumP 

–  This
is stimulated to divide to form an embryoP

–  The
embryo is placed in the uterus of another adultP

–  Embryo
develops normallyP

–  A
genetically identical baby will be bornP

STEM CELLS

–  Undifferentiated
cellsP

–  that
can be developed into any tissue typeP 

➢
Used for therapeutic purposes, like regenerating spinal tissue (for paralysis)
or pancreatic cells (for diabetes mellitus) 

SOURCES OF STEM CELLS 

➢  Umbilical
cord 

➢  Embryos 

➢  Bone
marrow 

EVOLUTION 

DIFFERENCES BETWEEN LAMARCKISM AND DARWINISM

DIFFERENCES BETWEEN NATURAL SELECTION AND
ARTIFICIAL SELECTION  

HOW
LAMARCK AND DARWIN EXPLAINED EVOLUTION (IN GENERAL)

*Evolution
according to Lamarck 

Lamarck explained evolution using the following two
‘laws’: 

The law of use and disuse: P 

–  As
an organism uses a structure or organ more regularlyP,
it becomes    better developed or
enlarged in that organismP. 

–  If
an organism does not use a structure or organ frequentlyP,
it becomes 

  less developed
or reduced in size and may disappear altogether in that organismP 

The law of inheritance of acquired
characteristics: P 

– Characteristics developed
during the life of an individualP-
(Acquired characteristics) can      be
passed on to their offspringP

*Evolution according to Darwin  

–  Organisms
produce a large number of offspringP 

–  There
is a great deal of variationP amongst the
offspring 

–  Some
have favourable characteristicsPand
some do not

–  When
there is a change in the environmental conditionsP/or
there is competition 

–  then
organisms with characteristics which are more favourable surviveP 

–  whilst
organisms with less favourable characteristics dieP 

–  This
is called natural selectionP 

–  The
organisms that survive reproduceP 

–  and
thus pass on the favourable characteristics to their offspringP 

–  The
next generation will therefore have a higher proportion of individuals with
the       favourable characteristicsP 

HOW LAMARCK AND DARWIN EXPLAINED EVOLUTION (SPECIFIC EXAMPLE) 

An ancestor of the elephant, Phiomia, had a long nose-like structure called a proboscis which
evolved into the trunk of the modern elephant. The proboscis was used to gather
leaves as food. 

Explain the evolution of the elephant’s trunk in terms
of Lamarckism and Darwinism as well as the way in which an increase in the
length of the trunk of the elephant could be achieved through artificial
selection.

Lamarckism:
 

–  The
ancestral elephant stretched its proboscisP 

–  to
get leavesP in trees/further from the
body 

–  The
more it used the proboscisP 

–  the
longer it becameP – law of use and disuse.  

–  The
offspring then inherited the acquired longer proboscis P-
law of inheritance of    acquired characteristics  

–  Over
many generations the length of the proboscis increasedP-
until it became a    trunkP as in the modern elephant 

Darwinism:
 

–  There
was a great deal of genetic variationP
amongst the offspring of the ancestral    
elephant

–  Some
had a long proboscisPand some had a short
proboscis 

–  There
was a change in environmental conditionsP/competition
amongst the animals     for food 

–  They
had to reach higher in the trees to get leavesP 

–  The
animals with shorter proboscis diedP
as they could not reach the leaves 

–  They
did not possess the favourable characteristics for that environment – Those
individuals with the longer proboscis survivedP
as they possessed the     favourable
characteristics for the environment.  –
The elephants with the longer trunks then reproducedP 

–  and
passed on this favourable characteristic to their offspringP 

–  The
next generation of animals had a greater proportionP
of longer trunks 

–  Gradually
over time the gene pool of the elephants with short trunks are eradicatedP 
Artificial selection:  

–  HumansPselect the elephants with 

–  desirable
characteristicsP/long trunk 

–  and
mate them to produce offspring with longer trunksP 

–  Those
that are pure breedingP for long trunks 

–  are
further selected to mate to produce offspring with further longer trunksP 
DARWIN’S IDEAS ABOUT GRADUALISM
COMPARED TO PUNCTUATED EQUILIBRIUM  

–  Darwin
believed that evolution takes place through an accumulation of smallP 

–  gradual
changes that occur over a long period of timeP 

–  supported
by transitional forms in fossil recordP 

–  Punctuated
equilibrium suggested that evolution sometimes involves long    periods of time where species do not changeP/very little change occurs  – This alternates with short periods of time
where rapid changes occurP  – New species are formed in a short period of
timeP/relative to the long    period of no/little change 

–  supported
by the absence of transitional formsP 

THE ROLE OF VARIATION IN NATURAL SELECTION

–  Organisms
of a particular species shows a great deal of variationP 

–  Some
individuals may have characteristics that are favourableP
/any example 

–  Others
may have characteristics that are unfavourableP
/any example 

–  If
there is competitionP/changing
environmental conditions/ selective pressure by the    environment 

–  organisms
with favourable characteristics surviveP 

–  and
reproduceP 

–  and
pass this favourable characteristics to their offspringP 

–  while
organisms with unfavourable characteristics will die outP 

–  Over
time the whole population will have this favourable traitP

DIFFERENCES BETWEEN A POPULATION AND A SPECIES  

–  A species is a group of organisms with
similar characteristicsP 

–  that
are able to interbreedP 

–  to
produce fertile offspringP 

–  A population is a group of organisms of
the same speciesP 

–  found
in the same habitat P 

–  at
the same timeP 

SPECIATION BY GEOGRAPHIC ISOLATION (IN GENERAL)  

•  If a
population splits into two populations P
by a geographical barrier 

•  there
is now no gene flow between the two populationsP 

•  Since
each population may be exposed to different environmental conditionsP

•  Natural
selection occurs independently in each of the two populationsP 

•  such
that the individuals of the two populations become very different from
each    otherP 

•  genotypicallyP and 

•  phenotypicallyP 

•  Even
if the two populations were to mix againP

•  they
will not be able to reproduce with each otherP
thus becoming different / new   
species 

SPECIATION BY GEOGRAPHIC ISOLATION (SPECIFIC
EXAMPLE)  

Use the example of the anole lizard of the Caribbean
Islands to describe how natural selection led to the process of speciation that gave rise to different
species of lizards. 

–  The
original species of anole lizards was separatedP 

–  into
different populationsP 

–  by a
geographical barrier P

–  which
is the sea P 

–  There
was no gene flowP 

–  between
the separated populationsP 

–  Each
population was exposed to different environmental conditionsP/ different    environmental temperatures and food
availability on each island 

–  Because
there is variationP amongst the
lizards 

–  natural
selection occurred independently P
in each population 

–  Each
population became different from the other P
over time 

–  genotypicallyP 

–  and
phenotypicallyP 

–  Even
if the populations were to mix againP 

–  they
would not be able to reproduce/interbreed with each otherP 

MECHANISMS FOR REPRODUCTIVE ISOLATION  

Geographic isolation causes speciation. Reproductive
isolation isolates the gene pool of a species. 

Examples of reproductive isolation: 

•  Breeding
at different times of the year 

•  Species-specific
courtship behaviour 

•  Adaptation
to different pollinators 

•  Infertile
offspring 

•  Prevention
of fertilisation

THE ROLE OF MUTATIONS AND EVOLUTION IN PRESENT
TIMES (IN GENERAL)  

–  In a
population of insectsP /bacteria/HI
viruses/Galápagos’ finches 

–  mutations
are a source of variation 

–  which
may make some organisms more resistant P
/better suited 

–  to
insecticidesP
/antibiotics/antiretroviral medication/ drought 

–  Those
individuals that are not resistant /suited will dieP
whereas 

–  those
that are resistant/ well suited, will surviveP 

–  to
pass the resistant allele/resistance on to their offspringP 

–  This
is known as natural selectionP 

–  As a
result, individuals of the future generations will be resistant to the    insecticidesP/antibiotics/antiretroviral
medication/adapted to drought

HOW MOSQUITOES DEVELOP RESISTANCE TO DDT
(SPECIFIC EXAMPLE)  

− More mosquitoes are produced than can surviveP 

− There is genetic variationP
amongst the mosquitoes

− Some mosquitoes may be naturally resistant to DDTP 

− When DDT is appliedP 

− those that are resistant surviveP 

− and they then reproduceP 

− passing the allele for resistance to the offspringP 

− Those that are not resistant, dieP 

− and their alleles are lost from the population. P 

− The number of DDT-resistant mosquitoes therefore
increases over the generationsP  EVIDENCE
FOR EVOLUTION, HUMAN EVOLUTION AND OUT OF AFRICA

HYPOTHESIS 

HUMAN EVOLUTION

CHARACTERISTICS
THAT HUMANS SHARE WITH AFRICAN APES.  

–  Large
brainsP / skulls compared to their body
mass 

–  BipedalP / upright posture / foramen magnum
in a more forward position 

–  Olfactory
brain centres reducedP/ reduced sense of
smell 

–  Eyes
in frontP/ binocular vision / stereoscopic
vision 

–  Eyes
with conesP / colour vision 

–  Freely
rotating armsP 

–  Long
upper armsP 

–  Five
digits per limbP 

–  Flat
nails instead of clawsP/ bare, sensitive
finger tips 

–  Opposable
thumbsP/precision grip 

–  Sexual
dimorphismP / distinct differences between
males and females 

ANATOMICAL DIFFERENCES BETWEEN HUMANS (Homo sapiens)  AND AFRICAN APES 

GENERAL TREND IN HUMAN EVOLUTION HAS BEEN
TOWARDS BIPEDALISM AND A CHANGE IN DIET FROM RAW FOOD TO COOKED FOOD

The
development of bipedalism:  

•  The
backward position of the foramen magnum on the skullP 

•  the
narrow pelvisP 

•  and
the less-curved spineP 

•  indicates
that the ape-like beings were quadrupedalP 

•  The
forward position of the foramen magnum on the skullP 

•  the
wider / shorter pelvisP 

•  and
the curved S- spineP 

•  indicates
that modern humans are bipedalP 

Change
in the diet from raw food to cooked food:  

•  The
large teeth, especially the caninesP 

•  as
well as the large and long jawsP 

•  which
makes the skull prognathousP 

•  as
well as cranial/brow ridges associated with large muscles that operate the jawsP 
• indicate that the ape-like beings ate raw food that required a great
amount of    processingP /tearing, biting and chewing.  • The smaller teeth, including the caninesP 

•  as
well as the smaller jaw sizeP 

•  which
makes the skull less prognathousP 

•  as
well as the absence of cranial/brow ridges due to the presence of smaller    muscles for chewingP 

•  indicate
that modern humans rely on a diet of cooked food that does not require the    same amount of processingP /tearing, biting and chewing. 

ADVANTAGES OF BIPEDALISM

–  Frees
the armsP so that they could carry offspringP/ tools / food / manipulate
things 

–  Allows
ability to see furtherPto spot dangerP/ food 

–  Exposes
a large surface areaP for thermoregulationP 
– Reduces the surface area exposed to the sunP
so less    heat is absorbedP/ less heat
lost/thermoregulation 

–  Expose
the genitalsPto attract opposite
sexP 

–  Efficient
locomotionPallows traveling over longer
distances 

ADVANTAGES OF LARGER CRANIUM  

–  Allows
for a bigger brainP 

–  Development
of speechP/ communication 

–  Higher
intelligenceP 

–  Complex
behaviourP 

–  Quick
processing of informationP 

–  Process
large amounts of information 

OUT OF AFRICA HYPOTHESIS  

–  All
modern humansP /Homo sapiens 

–  originated
in AfricaP 

–  and
migrated to other partsP of the world 

EVIDENCE
THAT SUPPORTS THE OUT OF AFRICA HYPOTHESIS: 

FOSSIL EVIDENCEP 

–  The
OLDEST Fossils of Ardipithecus were
found ONLY in AfricaP /Rift  

  Valley/Ethiopia/South
Africa 

–  The
OLDEST Fossils of Australopithecus
were found ONLY in AfricaP/Rift 

Valley/Ethiopia/South Africa 

–  The
OLDEST fossils of Homo habilis were
ONLY found in AfricaP 

–  The
OLDEST fossils of Homo erectus were
found in AfricaP 

–  The
OLDEST fossils of Homo sapiens were
found in AfricaP 

GENETIC EVIDENCEP 

–  Mitochondrial
DNAP 

–  is
passed down from mother to childP
/ is inherited only from the maternal line 

–  Analysis
of mutationsP on this
mitochondrial DNA 

–  were
traced to an ancestral female that existed in AfricaP 

–  and
shows that all humans descended from herP/mitochondrial
Eve 

–  The
Y chromosome shows the paternal lineP

CULTURAL EVIDENCEP 

–  The
OLDEST/most primitive artefacts (tools, cutlery, art etc.) 

–  were
ONLY found in AfricaP

September 3, 2023 getanswered 0 Comments

LIFE-SCIENCES-Grade-12-Study-Notes-P2-GET-ANSWEREDDownload

    BEHAVIOUR OF CHROMOSOMES

 DURINGTHE DIFFERENT PHASES OF

 MEIOSIS I

 

–  During
prophaseP I 

–  chromosomes
pairPup/homologous pairs /bivalents
form 

–  Crossing
overPexchange of genetic material
occurs 

–  between
chromatidsP/adjacent chromosome pairs 

–  During
metaphaseP I of meiosis 

–  homologous
chromosomesP/chromosome pairs are arranged 

–  at the equatorPof the cell 

–  in a
randomP way 

–  with
the chromosome attached to the spindle fibreP 

–  During
anaphase P I 

–  chromosome
pairs separateP/chromosomes move to
opposite poles 

–  During
telophase P I 

–  the
chromosomes reach the poles of the cellP 

 

EVENTS THAT LEAD TO DOWN SYNDROME

–  Non-disjunction
occurredP/A homologous pair of
chromosomes 

–  at
position 21P 

–  failed
to separateP 

–  during
anaphaseP 

–  resulting
in one gamete with 24 chromosomesP
/ an extra chromosome /    chromosomes at
position 21 

–  The
fertilisation of this gamete with a normal gameteP/gamete    with 23 chromosomes /1 chromosome at
position 21 

–  results
in a zygote with 47 chromosomesP 

–  There
are 3 chromosomesP/an extra chromosome
at position 21/ this is Trisomy 21 HOW
MEIOSIS CONTRIBUTES TO GENETIC VARIATION 

 Crossing
overP 

–  Occurs
during prophase IP 

–  Chromatids
of homologous chromosomes overlapP 

–  at
points called chiasmaP/ chiasmata 

–  Genetic
material is exchangedP 

–  resulting
in new combinations of genetic material Pfrom
both parents 

 Random
arrangement of chromosomes 

–  Occurs
during metaphase I P/ II 

–  Each
pair of homologous chromosomes P
/each chromosome 

–  may
line up in different waysP on the equator of
the spindle 

–  allowing
the gametes to have different combinations of maternal and paternal    chromosomes P 

–  so
that they separate in a randomP/
independent manner 

–  resulting
in new combinations of genetic materialP

HOW
MUTATIONS CONTRIBUTE TO GENETIC VARIATION  

 

Two types of mutations:  
gene mutation and


chromosome mutations

–  A geneP
mutation occurs 

–  as a
result of a change in sequence of nitrogenous basesP
in the DNA molecule 

– A chromosomePmutation occurs as a 

–  result
of a change in the structure of a chromosomePOR

–  a
change in the number of chromosomes during meiosisP 

– Mutations
that occur in sex cellsP 

–  are
passed on to the new generationsP 

–  creating
new characteristicsP 

DNA: CODE OF LIFE &
PROTEIN SYNTHESIS 

THE LOCATION, STRUCTURE AND FUNCTIONS OF A DNA
MOLECULE  

–  The
DNA is located in the nucleusP/chromosome/genes/mitochondria 

–  DNA
is a nucleic acidP 

–  It
is double strandedP molecule

–  and
arranged in the form of a helixP 

–  consisting
of building blocks called nucleotidesP    The three components of a nucleotide are as
follows: 

–  Nitrogenous
basesP 

–  Phosphate
portionP 

–  Deoxyribose
sugar portionP (in DNA) 

–  4
nitrogenous bases Pare A,T,C,GP  

–  adenine
(A) binds with thymine (T) P and cytosine (C)
binds with guanine (G)P 

–  by
weak hydrogen bondsP 

–  Sections
of DNA carry hereditaryPinformation 

–  DNA
contains coded information for protein synthesisP 

STRUCTURAL
DIFFERENCES BETWEEN DNA AND RNA.  

 

DNA	RNA
Double strandedP molecule	Single strandedPmolecule
Has a helixPshape	Is a straight moleculeP
One of the nitrogen bases is thymineP	The nitrogen base uracilPin place of thymine
Contains deoxyriboseP sugar	Contains ribosePsugar
A longerPmolecule	A shorterPmolecule
Paired basesP	Unpaired basesP

 

DNA REPLICATION

–  The
DNA- double helix molecule unwindsP
within the nucleus 

–  WeakP hydrogen bonds between the two
strands breakP/ the molecule
unzips 

–  Each
strand serves as a templateP to form a new strand

–  Free
DNA nucleotidesP attach to the
individual strands 

–  with
complementary nitrogenous basesP
pairing/ (A to T and C to G) 

–  Two
genetically identical DNA moleculesP
are formed 

–  Process
is controlled by enzymesP

EXTRACTING DNA (practical work)

SUBSTANCE	FUNCTION
Onion, strawberry, wheat germ etc.	Source of DNA
Dishwashing liquid	Breaks down cell membranes
Salt	Combines with nucleic acid to form visible  crystals, since DNA is not visible
Meat tenderizer, pineapple juice, contact lens solution	Contains enzyme to break down the histone proteins
Alcohol/ methylated spirits	DNA is NOT soluble in these solvents and will therefore appear as a stringy or cloudy mass

•             
Grating the onion, increases the surface area
for the dishwashing liquid, salt and    
tenderizer to act on. 

•             
Placing the beaker in hot water allows for the
cell breakdown to occur faster  TRANSCRIPTION IN PROTEIN SYNTHESIS

–  Occurs
within the nucleusP 

–  Double-stranded
DNA unwindsP 

–  and
unzipsP/2 DNA strands separate/the weak
hydrogen bonds break

–  One
strand is used as a templateP 

–  to
form mRNAP 

–  using
free RNA nucleotides from the nucleoplasmP 

–  The
mRNA is complementary to the DNAP/
A-U, C-G 

–  This
process is controlled by enzymesP 

–  The
coded message for protein synthesis is thus copied onto mRNAP 

–  Each
base triplet is called a codonP 

TRANSLATION IN PROTEIN SYNTHESIS

–  mRNA
moves from the nucleusP/to the ribosome
within the cytoplasm 

–  The
anticodon on the tRNA matches the codon on the mRNAP 

–  tRNA
brings the required amino acidP 

–  to
the ribosomeP 

–  Amino
acids are joined by peptide bondsP 

–  to
form the required proteinP/ polypeptide chain.

HOW A GENE MUTATION INFLUENCES THE STRUCTURE OF
A PROTEIN

–  A
mutation is a change in the nucleotide/nitrogenous base sequenceP 

–  of a
DNA moleculeP/a gene 

–  since
mRNA is copied from the DNA moleculeP 

–  during
transcriptionP 

–  This
will result in a change in the codonsP 

–  As a
result, different tRNAP molecules 

–  carrying
different amino acidsP will be
required 

–  The
sequence of amino acids changesP 

–  resulting
in the formation of a different proteinP 

–  If
the same amino acid P is coded for 

–  there
will be no changeP in the protein
structure 

USES OF DNA PROFILING / ANALYSIS  

–  To
investigate crimes P/ resolve
disputes 

–  To
identify organisms from their remainsP 

–  To
identify family relationships other than paternityP
e.g. siblings or cousins 

–  To
test for the presence of specific allelesP
/ genes that cause a genetic disorder – To establish matching tissues for organ
transplantsP 

GENETICS 

MENDEL’S LAW OF DOMINANCE

–  When
two organisms with pure breedingP
contrasting characteristics Pare crossed 

–  All
the individuals of the F₁ generation will display the dominant traitP 

  OR 

–  If
an organism is heterozygousP the 

–  dominant
alleleP will 

–  determine
the phenotypeP

MENDEL’S LAW OF INDEPENDENT ASSORTMENT  

–  The
various genes are separateP entities and do not
influence each other in any way 

–  They
sort themselves out independentlyP 

–  during
gamete formationP 

–  since
homologous chromosomes arrange themselves randomlyP
along the equator 

–  during
metaphase IP 

MENDEL’S LAW OF SEGREGATION

–  Each
characteristic is controlled by two genes situated on homologous chromosomesP 

–  During
meiosisP /anaphase/ when gametes form, 

–  the
two genes are separated or segregatedP 

–  enabling
a gamete to contain one of the two allelesP
from each parent

SUMMARY OF GENETIC CROSSES 

 

TYPE	DEFINITION	EXAMPLE
1) Complete dominance	Only one characteristic is expressed in the phenotype of a hybrid	TT x tt = Tt  (100% tall offspring)
2) Incomplete dominance	Neither allele is completely dominant over the other and both genes have equal influence in expressing the phenotype in the F1 generation	RR x WW = RW  (100% pink offspring)
3) Co-dominance	Different alleles of a hybrid are equally dominant over each other	RR x WW = RW  (100% roan offspring)
4) Sex linked inheritance	Genes which are carried on gonosomes , are referred to as sex linked genes or alleles	XHXh x XHY (haemophilia) = XHXH; XHXh; XHY; XhY
5) Dihybrid cross	A          cross         involving          2 characteristics at a time	RRYY x rryy = RrYy  (All round, yellow seeds)

 

WHY THE SEX OF A CHILD IS DETERMINED BY THE MALE
GAMETE

–  Normal
males have one X and one YP 

–  Normal
females have two XP chromosomes 

–  The
female always provides the X- chromosome in the ovumP 

–  If
an ovum is fertilized by an X bearing spermP    a female/girlP
is formed 

–  If
an ovum is fertilized by a Y bearing spermP 

–  a
male/boyP is formed 

WHY ARE THERE MORE MALES THAN FEMALES WITH
COLOUR-BLINDNESS  

–  Males
only have one X-chromosomeP 

–  If
this chromosome carries the recessive alleleP/X^b 

–  the
male will be colour-blindP 

–  the
Y-chromosome in males, does not carry any allele to mask the effect of the
colour-   blind alleleP 

–  Females
have 2 X-chromosomesP 

–  They
need to have two recessive allelesP/X^b
X^b to be affected 

–  A
dominant allele on the other X-chromosome will mask the effectP of the recessive    trait. 

A HAEMOPHILIAC FEMALE MARRIES A MALE WITHOUT
HAEMOPHILIA EXPLAIN WHY ALL THEIR SONS WILL BE HAEMOPHILIAC

–  An
individual inherits one allele from each parentP 

–  The
Y chromosome was inherited from the fatherP 

–  and
the recessive allele / X^h was inherited from the motherP 

–  since
the mother has two recessive allelesP/X^h
X^h 

–  A
son only needs to get one recessive allele to be haemophiliacP since the 

–  Y-chromosome
does not carry any allele to mask the effect of haemophilia alleleP

WHY FEMALES HAVE A SMALLER CHANCE OF SUFFERING
FROM HAEMOPHILIA  

–  Haemophilia
is caused by a recessive alleleP 

–  Carried
on the X chromosomeP 

–  Females
have two X chromosomesP/ Males only have one
X chromosome 

–  Females
must inherit two copies of the recessive alleleP 

  females who
inherit only one of the recessive alleles are still non-haemophiliacP 

GENETIC MODIFICATION

–  Removing
a useful gene from one organismP
and 

–  inserting
it into another organismP

–  to
produce beneficial characteristicsP

ADVANTAGES OF GENETIC ENGINEERING  

–  Production
of medicationP/ resources
cheaply 

–  Control
pests with specific genes inserted into a cropP 

–  Using
specific genes to increases crop yieldsP
/ food security  – Selecting genes to
increase shelf-life of plant productsP 

WHY SOME PEOPLE MAY BE AGAINST THE USE OF
GENETIC ENGINEERING

–  The
long-term effects on health are unknownP
which 

–  could
lead to health problems in the futureP 

–  The
long-term effects on biodiversityP/
damaging ecosystems/nature 

–  People
are morally opposedP as 

–  humans
are interfering with natureP/playing
God/interfering with the rights of every   
species 

–  Initially
it is an expensive processP and 

–  many
people/countries may not afford it /research money could be used for other
needs  CLONING  

–  A
somatic diploid cell from tissue is usedP  – The nucleus is removed from this cellP – and is placed inside an “empty”
ovumP 

–  This
is stimulated to divide to form an embryoP

–  The
embryo is placed in the uterus of another adultP

–  Embryo
develops normallyP

–  A
genetically identical baby will be bornP

STEM CELLS

–  Undifferentiated
cellsP

–  that
can be developed into any tissue typeP 

➢
Used for therapeutic purposes, like regenerating spinal tissue (for paralysis)
or pancreatic cells (for diabetes mellitus) 

SOURCES OF STEM CELLS 

➢  Umbilical
cord 

➢  Embryos 

➢  Bone
marrow 

 

 

EVOLUTION 

DIFFERENCES BETWEEN LAMARCKISM AND DARWINISM

LAMARCKISM	DARWINISM
Variation of the offspring occurs when  individuals in the population changeP	Variation in the offspring is inheritedP
Change occurs because of adaptation to the environmentP/ Law of use and disuse	Natural selection – individuals best suited to the environment surviveP
Individuals in the population changeP	The population as a whole changesP
Acquired characteristics are inherited by  offspringP	Characteristics are passed on from generation to generation to enable individuals to survive in the environmentP

DIFFERENCES BETWEEN NATURAL SELECTION AND
ARTIFICIAL SELECTION  

NATURAL SELECTION	ARTIFICIAL SELECTION
The environment Por nature is the selective force	HumansPrepresent the selective force
Selection is in response to suitability to the  environmentP	Selection is in response to satisfying human needsP
Occurs within a speciesP	May involve one or more species P (as in cross breeding)

HOW
LAMARCK AND DARWIN EXPLAINED EVOLUTION (IN GENERAL)

  

*Evolution
according to Lamarck 

Lamarck explained evolution using the following two
‘laws’: 

The law of use and disuse: P 

–  As
an organism uses a structure or organ more regularlyP,
it becomes    better developed or
enlarged in that organismP. 

–  If
an organism does not use a structure or organ frequentlyP,
it becomes 

  less developed
or reduced in size and may disappear altogether in that organismP 

The law of inheritance of acquired
characteristics: P 

– Characteristics developed
during the life of an individualP-
(Acquired characteristics) can      be
passed on to their offspringP

*Evolution according to Darwin  

–  Organisms
produce a large number of offspringP 

–  There
is a great deal of variationP amongst the
offspring 

–  Some
have favourable characteristicsPand
some do not

–  When
there is a change in the environmental conditionsP/or
there is competition 

–  then
organisms with characteristics which are more favourable surviveP 

–  whilst
organisms with less favourable characteristics dieP 

–  This
is called natural selectionP 

–  The
organisms that survive reproduceP 

–  and
thus pass on the favourable characteristics to their offspringP 

–  The
next generation will therefore have a higher proportion of individuals with
the       favourable characteristicsP 

HOW LAMARCK AND DARWIN EXPLAINED EVOLUTION (SPECIFIC EXAMPLE) 

An ancestor of the elephant, Phiomia, had a long nose-like structure called a proboscis which
evolved into the trunk of the modern elephant. The proboscis was used to gather
leaves as food. 

Explain the evolution of the elephant’s trunk in terms
of Lamarckism and Darwinism as well as the way in which an increase in the
length of the trunk of the elephant could be achieved through artificial
selection.

Lamarckism:
 

–  The
ancestral elephant stretched its proboscisP 

–  to
get leavesP in trees/further from the
body 

–  The
more it used the proboscisP 

–  the
longer it becameP – law of use and disuse.  

–  The
offspring then inherited the acquired longer proboscis P-
law of inheritance of    acquired characteristics  

–  Over
many generations the length of the proboscis increasedP-
until it became a    trunkP as in the modern elephant 

Darwinism:
 

–  There
was a great deal of genetic variationP
amongst the offspring of the ancestral    
elephant

–  Some
had a long proboscisPand some had a short
proboscis 

–  There
was a change in environmental conditionsP/competition
amongst the animals     for food 

–  They
had to reach higher in the trees to get leavesP 

–  The
animals with shorter proboscis diedP
as they could not reach the leaves 

–  They
did not possess the favourable characteristics for that environment – Those
individuals with the longer proboscis survivedP
as they possessed the     favourable
characteristics for the environment.  –
The elephants with the longer trunks then reproducedP 

–  and
passed on this favourable characteristic to their offspringP 

–  The
next generation of animals had a greater proportionP
of longer trunks 

–  Gradually
over time the gene pool of the elephants with short trunks are eradicatedP 
Artificial selection:  

–  HumansPselect the elephants with 

–  desirable
characteristicsP/long trunk 

–  and
mate them to produce offspring with longer trunksP 

–  Those
that are pure breedingP for long trunks 

–  are
further selected to mate to produce offspring with further longer trunksP 
DARWIN’S IDEAS ABOUT GRADUALISM
COMPARED TO PUNCTUATED EQUILIBRIUM  

–  Darwin
believed that evolution takes place through an accumulation of smallP 

–  gradual
changes that occur over a long period of timeP 

–  supported
by transitional forms in fossil recordP 

–  Punctuated
equilibrium suggested that evolution sometimes involves long    periods of time where species do not changeP/very little change occurs  – This alternates with short periods of time
where rapid changes occurP  – New species are formed in a short period of
timeP/relative to the long    period of no/little change 

–  supported
by the absence of transitional formsP 

 

THE ROLE OF VARIATION IN NATURAL SELECTION

–  Organisms
of a particular species shows a great deal of variationP 

–  Some
individuals may have characteristics that are favourableP
/any example 

–  Others
may have characteristics that are unfavourableP
/any example 

–  If
there is competitionP/changing
environmental conditions/ selective pressure by the    environment 

–  organisms
with favourable characteristics surviveP 

–  and
reproduceP 

–  and
pass this favourable characteristics to their offspringP 

–  while
organisms with unfavourable characteristics will die outP 

–  Over
time the whole population will have this favourable traitP

DIFFERENCES BETWEEN A POPULATION AND A SPECIES  

–  A species is a group of organisms with
similar characteristicsP 

–  that
are able to interbreedP 

–  to
produce fertile offspringP 

–  A population is a group of organisms of
the same speciesP 

–  found
in the same habitat P 

–  at
the same timeP 

 

SPECIATION BY GEOGRAPHIC ISOLATION (IN GENERAL)  

•  If a
population splits into two populations P
by a geographical barrier 

•  there
is now no gene flow between the two populationsP 

•  Since
each population may be exposed to different environmental conditionsP

•  Natural
selection occurs independently in each of the two populationsP 

•  such
that the individuals of the two populations become very different from
each    otherP 

•  genotypicallyP and 

•  phenotypicallyP 

•  Even
if the two populations were to mix againP

•  they
will not be able to reproduce with each otherP
thus becoming different / new   
species 

 

 

 

 

 

 

 

 

SPECIATION BY GEOGRAPHIC ISOLATION (SPECIFIC
EXAMPLE)  

Use the example of the anole lizard of the Caribbean
Islands to describe how natural selection led to the process of speciation that gave rise to different
species of lizards. 

–  The
original species of anole lizards was separatedP 

–  into
different populationsP 

–  by a
geographical barrier P

–  which
is the sea P 

–  There
was no gene flowP 

–  between
the separated populationsP 

–  Each
population was exposed to different environmental conditionsP/ different    environmental temperatures and food
availability on each island 

–  Because
there is variationP amongst the
lizards 

–  natural
selection occurred independently P
in each population 

–  Each
population became different from the other P
over time 

–  genotypicallyP 

–  and
phenotypicallyP 

–  Even
if the populations were to mix againP 

–  they
would not be able to reproduce/interbreed with each otherP 

 

MECHANISMS FOR REPRODUCTIVE ISOLATION  

Geographic isolation causes speciation. Reproductive
isolation isolates the gene pool of a species. 

Examples of reproductive isolation: 

•  Breeding
at different times of the year 

•  Species-specific
courtship behaviour 

•  Adaptation
to different pollinators 

•  Infertile
offspring 

•  Prevention
of fertilisation

THE ROLE OF MUTATIONS AND EVOLUTION IN PRESENT
TIMES (IN GENERAL)  

–  In a
population of insectsP /bacteria/HI
viruses/Galápagos’ finches 

–  mutations
are a source of variation 

–  which
may make some organisms more resistant P
/better suited 

–  to
insecticidesP
/antibiotics/antiretroviral medication/ drought 

–  Those
individuals that are not resistant /suited will dieP
whereas 

–  those
that are resistant/ well suited, will surviveP 

–  to
pass the resistant allele/resistance on to their offspringP 

–  This
is known as natural selectionP 

–  As a
result, individuals of the future generations will be resistant to the    insecticidesP/antibiotics/antiretroviral
medication/adapted to drought

  

HOW MOSQUITOES DEVELOP RESISTANCE TO DDT
(SPECIFIC EXAMPLE)  

− More mosquitoes are produced than can surviveP 

− There is genetic variationP
amongst the mosquitoes

− Some mosquitoes may be naturally resistant to DDTP 

− When DDT is appliedP 

− those that are resistant surviveP 

− and they then reproduceP 

− passing the allele for resistance to the offspringP 

− Those that are not resistant, dieP 

− and their alleles are lost from the population. P 

− The number of DDT-resistant mosquitoes therefore
increases over the generationsP  EVIDENCE
FOR EVOLUTION, HUMAN EVOLUTION AND OUT OF AFRICA

HYPOTHESIS 

EVOLUTION	HUMAN EVOLUTION	OUT OF AFRICA HYPOTHESIS
Fossil evidence	Fossil evidence	Fossil evidence
Genetics	Genetics, mtDNA	Genetics, mtDNA
Comparative anatomy  (modification by descent)	Cultural evidence (tool making)	Cultural evidence (tool making)
Biogeography	Biogeography	Biogeography

 

 

HUMAN EVOLUTION

  

CHARACTERISTICS
THAT HUMANS SHARE WITH AFRICAN APES.  

–  Large
brainsP / skulls compared to their body
mass 

–  BipedalP / upright posture / foramen magnum
in a more forward position 

–  Olfactory
brain centres reducedP/ reduced sense of
smell 

–  Eyes
in frontP/ binocular vision / stereoscopic
vision 

–  Eyes
with conesP / colour vision 

–  Freely
rotating armsP 

–  Long
upper armsP 

–  Five
digits per limbP 

–  Flat
nails instead of clawsP/ bare, sensitive
finger tips 

–  Opposable
thumbsP/precision grip 

–  Sexual
dimorphismP / distinct differences between
males and females 

 

ANATOMICAL DIFFERENCES BETWEEN HUMANS (Homo sapiens)  AND AFRICAN APES 

 

FEATURE	HUMANS (Homo sapiens)	AFRICAN APES
Cranium	Large cranium P/ brain	Small cranium P/ brain
Brow ridges	Brow ridges are not wellP developed	Brow ridges are well Pdeveloped
Spine	More curved (S-shaped) Pspine	Less curved (C-shaped) P spine
Pelvic girdle	Short, wide pelvisP	Long, narrow pelvisP
Canines	Small caninesP	Large caninesP
Palate shape	Small and rounded palateP	Long and rectangular palateP
Jaws	Small jawsP  less protruding / less prognathous	Large jawsP  more protruding / more prognathous
Cranial ridges	No cranial ridgeP	Cranial ridge at the top of the craniumP
Foramen magnum	In a forward positionP	In a backward positionP below the skull

 

 

GENERAL TREND IN HUMAN EVOLUTION HAS BEEN
TOWARDS BIPEDALISM AND A CHANGE IN DIET FROM RAW FOOD TO COOKED FOOD

The
development of bipedalism:  

•  The
backward position of the foramen magnum on the skullP 

•  the
narrow pelvisP 

•  and
the less-curved spineP 

•  indicates
that the ape-like beings were quadrupedalP 

•  The
forward position of the foramen magnum on the skullP 

•  the
wider / shorter pelvisP 

•  and
the curved S- spineP 

•  indicates
that modern humans are bipedalP 

 

Change
in the diet from raw food to cooked food:  

•  The
large teeth, especially the caninesP 

•  as
well as the large and long jawsP 

•  which
makes the skull prognathousP 

•  as
well as cranial/brow ridges associated with large muscles that operate the jawsP 
• indicate that the ape-like beings ate raw food that required a great
amount of    processingP /tearing, biting and chewing.  • The smaller teeth, including the caninesP 

•  as
well as the smaller jaw sizeP 

•  which
makes the skull less prognathousP 

•  as
well as the absence of cranial/brow ridges due to the presence of smaller    muscles for chewingP 

•  indicate
that modern humans rely on a diet of cooked food that does not require the    same amount of processingP /tearing, biting and chewing. 

 

ADVANTAGES OF BIPEDALISM

–  Frees
the armsP so that they could carry offspringP/ tools / food / manipulate
things 

–  Allows
ability to see furtherPto spot dangerP/ food 

–  Exposes
a large surface areaP for thermoregulationP 
– Reduces the surface area exposed to the sunP
so less    heat is absorbedP/ less heat
lost/thermoregulation 

–  Expose
the genitalsPto attract opposite
sexP 

–  Efficient
locomotionPallows traveling over longer
distances 

ADVANTAGES OF LARGER CRANIUM  

–  Allows
for a bigger brainP 

–  Development
of speechP/ communication 

–  Higher
intelligenceP 

–  Complex
behaviourP 

–  Quick
processing of informationP 

–  Process
large amounts of information 

OUT OF AFRICA HYPOTHESIS  

–  All
modern humansP /Homo sapiens 

–  originated
in AfricaP 

–  and
migrated to other partsP of the world 

EVIDENCE
THAT SUPPORTS THE OUT OF AFRICA HYPOTHESIS: 

FOSSIL EVIDENCEP 

–  The
OLDEST Fossils of Ardipithecus were
found ONLY in AfricaP /Rift  

  Valley/Ethiopia/South
Africa 

–  The
OLDEST Fossils of Australopithecus
were found ONLY in AfricaP/Rift 

Valley/Ethiopia/South Africa 

–  The
OLDEST fossils of Homo habilis were
ONLY found in AfricaP 

–  The
OLDEST fossils of Homo erectus were
found in AfricaP 

–  The
OLDEST fossils of Homo sapiens were
found in AfricaP 

GENETIC EVIDENCEP 

–  Mitochondrial
DNAP 

–  is
passed down from mother to childP
/ is inherited only from the maternal line 

–  Analysis
of mutationsP on this
mitochondrial DNA 

–  were
traced to an ancestral female that existed in AfricaP 

–  and
shows that all humans descended from herP/mitochondrial
Eve 

–  The
Y chromosome shows the paternal lineP

CULTURAL EVIDENCEP 

–  The
OLDEST/most primitive artefacts (tools, cutlery, art etc.) 

–  were
ONLY found in AfricaP

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• GRADE 12

1 thought on “LIFE SCIENCES GRADE 12 – PAPER 2 SHORT ANSWERS”

1. Thank you sir now I have hope to pass life sciences with good marks

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