Lecture 2 hereidity and variation, ,heredity and variation ,variation ,what variations can you see...
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Transcript of 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