For IGCSE O-Level Biology students Chapter 15

1. VARIATION AND
EVOLUTION

2. Variation
 There are different
characteristics with
many intermediates
in between.
 E.g. height, weight,
skin colour …etc
 Caused by different
genes as well as
different
environment.
 There are different
characteristics with
no intermediates in
between.
 E.g. blood types,
eye colour…etc
 Caused by different
genes
Continuous
variation
Discontinuous
variation

3. Diagrams representing
variation
Continuo
us
variation
histogra
m

4. Diagrams representing
variation
Discontinuou
s variation
Bar chart,
bars
seperate
d

6.  Count the number of tongue rollers and non
tongue rollers in class.
 What type of variation does this characteristic
show?
 Can you tell what causes this type of variation?
 Can you find out which characteristic is
dominant?
Tongue roller or not?
Tongue roller Non tongue roller

7. Mutation
 A sudden unpredictable change in genes or
chromosomes of an organism.
 Mutation can be due to a mistake that takes
place during copying the DNA during cell
division.
 Mutagens can increase the chance of
mutation, examples of mutagens are ionising
radiations:
UV rays, gamma rays, x-rays, and chemicals:
tar, mustard gas.

8. A condition caused by an inherited gene that
cannot produce the brown pigment in the skin
and hair called melanin.
Albinism

9. A condition caused by a mistake during egg
formation, which produces an egg with 24
chromosomes, upon fertilisation a zygote with 47
Down’s syndrome

10. Black & peppered moths.
Peppered moth
Black moth

11. Can mutation be useful?

12.  Is when nature (conditions in the environment)
favours the survival of an organism that is more
suited to that environment.
 This causes the evolution of an organism with
time, so that the better suited (adapted) with
better genes survive and the one that is less
adapted becomes extinct.
Natural selection

13. Artificial selection
 Is when humans chose which two organisms
interbreed to produce an offspring with a
desired set of genes.
 Widely used by farmers to produce a breed
that can produce more milk, or better meat or
more wool, bigger eggs …etc
 Plants can be artificially selected
by crossing the desired flowers to
get new offspring with better traits.

14. Bacterial resistance