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Variation and selection
What do you mean by variation..?
Differences between species
Differences within
a species
VARIATIONS:
SPECIES : A species is a
group of organisms that
are able to interbreed and
produce fertile offspring.
Causes of variation : Genetic causes
Causes of variation : Environmental causes
1.Climate,
2.Diet,
3.Accidents,
4.Culture and
5.Lifestyle.
Causes of variation : Both genetic and environmental
a person might inherit a
plants may have the potential for
tendency to be tall, but a
strong growth, but if they do not
poor diet during
receive sufficient mineral
childhood will cause poor
resources from the soil, they may
growth
hardly grow at all
CONTINUOUS VS DISCONTINUOUS VARIATION
Variation, the small
differences that exist
between individuals, can
be described as being
either discontinuous
or continuous.
Continuous variation
1. Continuous variation shows a complete range of the characteristics within a
population.
Example:
a) Height is an of continuous variation - individuals can have a complete range
of heights, for example, 1.6, 1.61, 1.62, 1.625 etc meters high.
b) Weight;
c) Hand span
d) Shoe size
Continuous variation is the combined effect of many genes (known as polygenic
inheritance) and is often significantly affected by environmental influences.
Discontinuous variation
Discontinuous variation
1. This is where individuals fall into a number of distinct classes or categories, and is
based on features that cannot be measured across a complete range.
2. There are no intermediates between categories.
3. You either have the characteristic or you don't.
Examples:
a) Blood groups are a good example: you are either one blood group or another - you
can't be in between. Such data is called discrete (or categorical) data.
1. Discontinuous variation is controlled by alleles of a single gene or a small number of genes.
2. The environment has little effect on this type of variation.
17.2 MUTATION
Protein synthesis
What Are Mutations?
• A mutation is a spontaneous change in a gene or a
chromosomes.
Types of mutation
1. Gene Mutation
• Change in the nucleotide sequence of a gene
• May only involve a single nucleotide.
Gene Mutation Examples
1. Gene mutation in drosophila
2. Albino
3. Sickle cell anemia
Describe the features of sickle cell anaemia.
1. fewer red blood cells
2. less elastic / less flexible / sickle-shaped, red blood cells
3. haemoglobin is abnormal shape
4. haemoglobin / blood, less efficient at transporting oxygen
5. less respiration
6. less energy / fatigues / exhaustion / less active /
7. feeling faint / breathlessness
8. death of tissues linked to oxygen supply
9. capillaries are blocked
10. ‘sickle cell crisis’
11. slow / poor, growth
12. susceptible to infections
13. reduced life span
Example : Sickle cell anaemia
Sickle cell
Sickle cell anaemia & its incidence in relation to that of
malaria
Explain why HbS is more common in parts of tropical Africa
Chromosome
: Structure
TypesMutation
of mutation
2. Chromosome Mutation :
Structural and numerical
The loss or gain of part of a chromosome
Changing the structure or number of a chromosome
2. Chromosome Mutation : Number
Causes of mutation
• Mutagens such as:
1. Naturally: DNA replication error
2. X-rays
3. UV rays
4. Chemicals (tobacco smoke)
Are Mutations Helpful or Harmful?
• Often mutation can be harmful.
• Some mutation are beneficial .
• Some mutation have no effect at all.