Variation

1. LEARNING OBJECTIVES:
1.Understanding variation in organisms
2.Understanding the causes of variation
3.Being respectful towards one another despite variation
VARIATION
The difference between organisms of the
same species.

2. Continouos variation is the variation
that have range of values from the
smallest o the biggest .
Eg. shortest – tallest
lightest - heaviest
Discontinuous variation – which have no
range: you either have the characteristic
,or you do not OR you can do something
or you cannot.

3. Examples of continuous
variation
Exapmles of discontinuous
variation

4. CAUSES OF VARIATION
GENETIC FACTORS ENVIRONMENTAL FACTORS
Crossing -over
Independent assortment
mutations
Random fertilisation
Nutrition temperature light
intensity

12. CAUSES OF VARIATION
Environmental

13. GENE MUTATION – (point mutation) occurs at a single locus or gene
position on a chromosomes
- Sickle – cell anaemia
- Albinism
- Hutchinson –Gilford Progeria syndrome ( rapidly ageing )
-Polydactylism
CHROMOSOMAL MUTATION :
1. Increase or decrease in the number of chromosomes
-Down’s syndrome (47 hromosomes)
-Turner’s syndrome (45 chromosomes)
-Triploid (3n)
-Tetraploid (4n)
Polyploidy – is common among flowering plants and food plants like
apples ,tomato and wheat
polyploidy
2. A change in the structure of the chromosomes – rearrangement of whole
blocks of gene son a chromosomes.

23. The importance of variation
in the survival of a species.
The moth exists in two forms ,grey
and dark melanic.
The grey Biston well carmouflaged
against lichen – covered tree trunks
In unpolluted enviroments, giving them
protection from predators.
However, in such unpolluted
environments , dark melanic Biston are
not carmouflaged and their numbers
decrease drastically due to
predation.
In 1940s ,the onset of Industrial Revolution
in England, air quality declined and soot
was deposited on tree trunk , killing lichen
and the grey moths were not carmouflaged
the melanic moths became dominant
until 1960s when the Clean Air Act was
introduced in the cities. After that the
quality improved and the number of
melanic moths decreased.