lecture 2 hereidity and variation, ,heredity and variation ,variation ,what variations can you see...

Heredity and variation

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 ?

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

© Biophoto AssociatesTiger moths

These tiger moths are from the same family

What variations can you see?

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

What variations can you see ?

Human variations

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

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

Acquired characteristics cannot be inherited

Acquired characteristics

Upper branches

lower branches

Apples

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.

The lower branches will receive less sunlight because ofthe shade cast by the upper branches.

The differences will not be inherited

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

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 brown. People do not belong to one or other distinct categories

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

Continuous variation

Hair colour variation

There are as many categoriesof hair colour asthere are children

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

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

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

percentagein populationof Britain

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

Blood groups