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

© Jane B

urton

These snails are all the same species (Cepaea nemoralis) but they vary considerably

What variations can you see ?

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The snails’ shells vary in

•the presence or absence of bands

•the number of bands

• their colour

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© Biophoto Associates

Tiger moths

These tiger moths are from the same family

What variations can you see?

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The uppermost moth is larger than the other two

The dark bands on the abdomen differ in number and thickness

The patterns of the forewings are quite different from each other

The number, shape and distribution of the black spots on the hind wings differ

The amount of orange colour in the hind wings varies

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You will already be familiar with many of the variations between individuals of the human species (Homo sapiens)

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

What variations can you see ?

Human variations

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Variations may be inherited or acquired

Inherited variations result from the activity of genesThey 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

Acquired & inherited

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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

Acquired characteristics

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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

Apples

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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

Environmental conditions

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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

Heredity & environment

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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(See ‘Heredity’ slide 19)

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

Discontinuous variation

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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

Blood groups

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Continuous variation describes the situation in which there area great many intermediates between the extremes

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

Hair colour variation

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

See slide 13 for other examples

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

Graph of heights

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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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Answer

Correct

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Answer

Incorrect

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