2. LE AR N IN G O U TC O M E S
• T st t t fa or ca v r t
o ae he ct s using aiaion;
• T expl in t effect ofgenet fa or on v r t
o a he s ic ct s aiaion;
• T expl in t effect ofenv onment lfa or on v r t
o a he s ir a ct s aiaion;
• T expl in t effect ofint a ion bet een genet fa or &
o a he s er ct w ic ct s
env onment lfa or on v r t
ir a ct s aiaion;
• T expl in mut t
o a aion;
• T expl in t impora ofv r t in t sur iv lofaspecies.
o a he t nce aiaion he v a
3. C A US E S OF
V A R I A T I ON
• Both genetic & environmental factors.
• Phenotype = genetic factors +
environmental factors
4. C A US E S OF
V A R I A T I ON
Genetic Environmenta
factors l factors
S exual
Mutation
reproduction
Independent Crossing Random
assortment over fertilisation
Gene Chromosomal
mutation mutation
5. The effects of genetic factors
• CROSSING OVER
– An exchange of portion of
chromatids between homologous
chromosomes.
– During Prophase I.
– Point of crossover are called
chiasmata.
– Enables maternal & paternal
alleles to mix.
6. • INDEPENDENT ASSORTMENT
– During Metaphase I the bivalents
of homologous chromosomes can line
up in any orientation on the
equator of the spindle.
– The number of possible
orientations = the number of pairs
of chromosomes.
– Human, 23 pairs = 223 (8,388,608
combination) even in the absence
of crossing over.
– The maternal & paternal
chromosomes are mixed up in the
gamete.
7. • RANDOM FERTILISATION
–Two gametes fuse to form a
zygote
–Any of the numerous male
gametes can fertilise any
of the female gametes
every zygote is
genetically unique.
8. The effects of
environmental factors
• R t ev yfa orw infl
efer o er ct hich uences t or nism fr t out
he ga om he side.
• E mpl : nutient t
xa es r s, emper t e, pH, w t , sunl , &ot st i.
aur aer ight her imul
9. N u t r ie n t s
• Influence their growth.
• Identical twins may differ in size &
ability to fight off diseases due to
different diets.
• Lack of certain nutrients can lead to
various diseases.
10. Light
• In a few varieties of corn, a
red pigment develops only in
parts of plant that is exposed
to sunlight.
• The darkening of human skin
when exposed to light shows a
change of phenotype due to an
environmental factors.
11. pH
• The plant Hydrangea macrophylla has
either pink / blue flowers.
• Flowers colour is determined by soil pH.
(acidic = blue, alkaline = pink)
12. MUTATION
• A spontaneous change in the
genetic material (DNA) of a
cell or organism.
• Two types :
a) Chromosomal mutation
b) Gene mutation
13. • May occur in somatic cell or
gametes.
• Gametes inherited from
generation to generation
• Somatic cells not passed on to
the next generation.
14. CHROMOSOMAL MUTATION
• Occurs when the structure of a
whole chromosome / set of
chromosomes is altered in some
way.
• DELETION : when a chromosome
breaks in two places & the section in
the middle is lost as the part rejoin.
16. • INVERSION : when a chromosome
breaks in two places & the middle
piece is reinserted with the sequence
of genes reversed.
17. • TRANSLOCATION : when a section
of one chromosome breaks off &
becomes attached to another
chromosome.
• DUPLICATION : when a section of
chromosome is copied twice.
18.
19. • Another kind of chromosome abnormality is
caused by the addition / loss of one @ more
whole chromosomes non-disjunction.
• When pairs of chromosomes fail to separate
during meiotic division. some gametes
get both chromosomes while others receive
none.
• Examples of chromosomal mutation :
Down’s syndrome, Klinefelter’s syndrome &
Turner’s syndrome.
20. GENE MUTATION
• A change in the base sequence of
DNA.
• ADDITION
– When an extra nucleotide sequence is
inserted into the chain.
• DUPLICATION
– When a portion of a nucleotide chain
is repeated.
21. • DELETION (β-thalassaemia)
– When a portion of the nucleotide
chain is removed from the sequence.
• INVERSION
– When a nucleotide sequence separates
from the chain, then rejoins its
original position but in an inverted
manner.
• SUBSTITUTION (sickle-cell anaemia)
– When one of the nucleotides is
replaced by another which has a
different nitrogenous base.
22. EXAMPLES OF GENE
MUTATION
• Sickle-cell anaemia
– Incorrect a.a. in haemoglobin.
– RBC to become sickle-shape low
binding capacity for oxygen die
• Cystic fibrosis
– Produce excessively thick & sticky
mucus closes the lungs & pancreas
impaired breathing & digestion
– Production of salty sweat upsets
the balance of minerals
23. M U TA G E N S
• Ag e n t s t h at i n d u c e
mu t at i o n s .
• I n d i vi d u al s wh o h ave
u n d e r g o n e mu t at i o n
MUTANTS
• D i vi d e d i n t o 2 = r ad i at i o n
& c h e mi c al s
24. RADIATION
• Ionising m utagens : X -rays, cosm ic
rays, & α-, β-, γ-rad iation from
rad ioactive isotopes.
• N on-ionosing m utagens : U ltraviolet
rad iation
25. C H E M IC A L S
• N itrous acid , colchicine, m ustard gas &
cigarette sm oke.
• N itrous acid alters a nitrogenous base in the
D N A m olecule.
• C olchicine prevents spind le form ation in
m itosis d oubles the chrom osom e num ber
in a d aughter cell.
26. IM P O R T A N C E O F
V A R IA T IO N
• The variable traits improve an
individual’s chance of survival &
success rate in reproduction.
• A better chance that some of the
individuals could be resistant to the
disease & survive (not like the clone).
