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Causes of variation

Two main factors:

1. Genetic factors

2. Environmental factors

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1. Genetic factors

Influenced by crossing-over,

independent assortment, mutation and

random fertilisation

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Crossing over, independent assortment and fertilisation.

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Genetic variation caused

by mutation Mutation sudden permanent change in the

nucleotide sequence of the DNA or in theamount of DNA.

Two types:1. Gene mutation

2. Chromosome mutation

Mutation can cause by:

1. Chemical or physical agents (mutagens)2. Mistakes that occur during DNA replication

3. Uneven distribution of the chromosomes duringcell division

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2. Environmental factors

Caused by surrounding condition such as:1.Water

2.Sunlight

3.Nutrients

4.pH

5.Temperature

The effect depends on how much condition

received by an organism during growth

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E.g.

- Chinese primrose (Primula sinensis) willproduce white flower when grow in a

warm temperature and will produce red

flower when grow in cool temperature.

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Environmentally induced cannot be

passed to offspring but genetic variationcan be inherited

Some variation in characteristics results

from interaction between genetic and

environmental factors

E.g. the action of sunlight on genes for

lighted-coloured skin may result in

darker skin

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What are the importanceof variation in the survival

of a species? Provides the necessary adaptations

for the species to compete and

survive. Essential for survival of the species.

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Exercise

Do Checkpoint 6.2 on page 202 inthe textbook