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

© Jane Burton Banded snails These snails are all the same species (Cepaea nemoralis) but they vary considerably What variations can you see ? 2

The snails’ shells vary in the presence or absence of bands the number of bands their colour 3

© Biophoto Associates Tiger moths These tiger moths are from the same family What variations can you see? 4

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 5

You will already be familiar with many of the variations between individuals of the human species (Homo sapiens) 6

There are variations in skin colour, hair colour, hair curliness, eye colour and sex What variations can you see ? Human variations 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 Acquired & inherited 8

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 9

The next side shows apples collected from different positions on the same tree The differences between the apples are acquired during the growing season The differences will not be inherited 10

North side, upper branches South side upper branches North side, lower branches South side, lower branches © Horticultural Research International Apples 11

What environmental conditions in the different parts of the 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 of the shade cast by the upper branches. This effect will be more pronounced on the North side Environmental conditions 12

A great many variations are influenced by both genetic and 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 13

Discontinuous variation Discontinuous variations are entirely genetically controlled They 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 14

percentage in population of Britain Discontinuous variation in blood group. The figures cannot be made to fit a smooth curve because there are no intermediates Blood groups 15

Continuous variation describes the situation in which there are a great many intermediates between the extremes For example, there is every shade of hair colour between black and blond. People do not belong to one or other of a small number of 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 variation 16

Hair colour variation There are as many categories of hair colour as there are children 17

Continuous variation also occurs when the characteristics are 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 18

thousands of men height in inches There seem to be distinct categories of height but this is because measurements are made to the nearest inch Graph of heights 19

If measurements could be made to the nearest millimetre there would be a smooth transition in the heights 20

This is how continuous variation would appear in a graph 21

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 22

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 23

Question 3 Which of the following can be changed by conditions other than genetic? (a)Blood group (b) Weight (c) Physique (d) Finger prints 24

Question 4 Which of the following are acquired characteristics ? (a)Lung cancer (b) Athleticism (c) Curly hair (d) Big feet 25

Question 5 Discontinuous variations are … (a) inherited (b) not inherited (c) a combination of inherited and acquired factors (d) acquired during a lifetime 26

Question 6 Which of the following are examples of continuous variation ? (a) Height (b) Weight (c) Sex (d) Intelligence 27

Answer Correct 28

Answer Incorrect 29