Within a species there is usually a great deal of variation between individuals

There are variations in skin colour, hair colour, hair curliness, eye colour and sex

What variations can you see ? 7

Variations may be inherited or acquired

•Inherited variations result from the activity of genes-They are genetically controlled

- Genetically controlled variations cannot be altered

For example, hair colour, skin colour*, blood group,finger prints and sex cannot be changed naturally

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Acquired characteristics result from an individual’s activities or nutrition or from environmental conditions during a lifetime

Examples of acquired conditions in humans are* -language -obesity -athletic skills -mental skills -body building -sun tan -Acquired characteristics cannot be inherited

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-The next side shows apples collected from differentpositions on the same tree

-The differences between the apples are acquired during the growing season

-The differences will not be inherited

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North side, upper branches South side upper branches

North side, lower branches South side, lower branches

© Horticultural Research International

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•What environmental conditions in the different parts ofthe tree might have caused the differences in size of the apples ?

-The upper branches will receive more sunlight than the lower branches, but on the North side the sunlight would have been less intense

-The lower branches will receive less sunlight because ofthe shade cast by the upper branches. This effect will be more pronounced on the North side

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•A great many variations are influenced by both geneticand environmental effects.

-For example your height will depend on what genes you inherit and the amount of food you get during your growing period

-You may inherit a good physique but unless you take exercise you will not develop to your full potential

-You may inherit the genes to make the pigment, melanin, in your skin but you will need to expose your skin to sunlight to acquire a tan

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Discontinuous variation

•Discontinuous variations are entirely genetically controlledThey cannot be altered by external conditions.

•You are either male or female, there are no intermediates

•Your ABO blood group is either A, B, AB or O

•Genetic defects such as colour blindness, albinism,achondroplastic dwarfism, sickle cell anaemia are all Genetically controlled and expressed in a discontinuous way.

•You either have these conditions or you do not. There are no intermediate states

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percentagein populationof Britain

Discontinuous variation in blood group. The figures cannotbe made to fit a smooth curve because there are no intermediates

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-Continuous variation is influenced by genes and environment, resulting in a range of phenotypes between two extremes,e.g. height in humans.

-For example, there is every shade of hair colour between blackand blond. People do not belong to one or other of a small numberof distinct categories.

-Variations such as these are under genetic control but there are several pairs of genes involved.

-The genome AA BB CC DD might give black hair while the genome aa bb cc dd might give blond hair.*

-Genomes AaBbCcDd or AABbCCdd or aaBBccDd and all the other possible combinations would give intermediate colours

Continuous variation16

There are as many categoriesof hair colour asthere are children

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Continuous variation also occurs when the characteristicsare controlled by the genes and the environment

-Your height will depend on the genes you inherit and on the amount of food you eat during your growing period

The next slide shows the range of heights of army recruits

Continuous variation

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thousandsof men

height in inches

There seem to be distinct categories of height but this is becausemeasurements are made to the nearest inch

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If measurements could be made to the nearest millimetrethere would be a smooth transition in the heights

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This is how continuous variation would appear in a graph

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Question 1

Which of these statements are correct?

(a) Wild plants of the same species do not vary

(b) There is always variation between individuals of the same species

(c) Individuals in the same species may show variations

(d) Daschunds and greyhounds are varieties of the same species

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Question 2

Variations in an individual’s weight…

(a) are entirely genetically controlled

(b) result exclusively from the amount of food taken in

(c) are the result of food intake and genes

(d) are the result of chance

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Question 3

Which of the following can be changed by conditions other than genetic?

(a) Blood group

(b) Weight

(c) Physique

(d) Finger prints

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Question 4

Which of the following are acquired characteristics ?

(a) Lung cancer

(b) Athleticism

(c) Curly hair

(d) Big feet

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Question 5

Discontinuous variations are …

(a) inherited

(b) not inherited

(c) a combination of inherited and acquired factors

(d) acquired during a lifetime

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Question 6

Which of the following are examples of continuous variation ?

(a) Height

(b) Weight

(c) Sex

(d) Intelligence

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