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Variation  
 

Variation  

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

•  Investigating  variation  
•  Types  of  variation  

Variation  
 

Sampling  

Investigating  Variation  
 

•   This  is  taking  measurements  of  individuals,  selected  from  the  population  
of  organisms  which  is  being  investigated
...
 This  is  because:  
-­‐   Sampling  bias:  Investigators  may  be  making  unrepresentative  
choices  either  knowingly  or  unwittingly
...
g
...
 E
...
 the  flowers  selected  may  just  happen  to  be  the  tallest  
in  the  area
...
 This  can  be  carried  out  by  random  sampling:  
1
...
 Using  random  numbers  from  a  random  number  generator  to  select  
the  coordinates  
3
...
 E
...
 much  smaller  
chance  that  500  flowers  will  be  the  tallest  than  just  50  flowers
...
 
-­‐   Analysis  of  data  collected:  Analysing  the  data  means  that  we  can  
use  statistical  tests  to  determine  whether  the  extent  to  which  
chance  has  influenced  the  data
...
 
 
 
Variation  is  the  result  of  two  factors:  genetic  differences  and  environmental  
influences
...
 
 

Genetic  Differences  
•   Due  to  the  different  genes  that  each  individual  possesses
...
 
•   It  arises  as  a  result  of:  
-­‐   Mutations:  Sudden  changes  to  genes  and  chromosomes  may,  or  
may  not,  be  passed  onto  the  next  generation
...
 Mixes  up  genetic  material  before  it  is  
passed  into  the  gametes,  meaning  that  they  are  all  therefore  
different
...
 Fusion  is  
also  random,  further  adding  to  the  genetic  diversity  of  the  
offspring
...
   
•   Sexually  reproducing  organisms  increase  variety  by  all  three  methods
...
 
 

Environmental  Influences  

 
 

•   Environmental  influences  affect  the  way  an  organisms  genes  are  
expressed
...
 
•   Environmental  factors  include  climatic  conditions  (temperature,  rainfall,  
sunlight),  soil  conditions,  pH  and  food  availability
...
 
•   Difficult  to  distinguish  between  the  two  and  so  hard  to  draw  conclusion  
about  the  causes  of  variation  in  an  area
...
 

 
 

Variation  
 

Types  of  Variation  
 

Variation  Due  to  Genetic  Factors  

 

•   When  variation  is  due  to  genetic  factors,  characteristics  fit  into  a  few  
distinct  forms  and  there  are  no  intermediate  types
...
 
•   A  character  displaying  this  type  of  variation  is  usually  controlled  by  a  single  
gene
...
   

Variation  Due  to  Environmental  Influences  
•   Some  characteristics  of  organisms  grade  into  one  another,  forming  a  
continuum
...
 
•   Characters  displaying  this  type  of  variation  are  not  controlled  by  a  single  
gene,  but  many  genes
...
 
•   This  type  of  variation  is  due  to  the  product  of  polygenes  and  the  
environment
...
 
 
 

Mean  and  Standard  Deviation  

Normal  distribution  curves  are  different  in  two  measurements:  maximum  height  
and  width
...
 Mean  of  
sample  data  provides  an  average  value  and  is  useful  when  comparing  
samples
...
   
•   Standard  Deviation:  measure  of  the  width  of  the  curve
...
 Distance  mean  to  to  point  where  curve  
changes  from  convex  to  concave
...
g
...
 Calculate  the  mean  value  (x’):    4  +  1  +  2  +  3  +  5  +  0  =  15  
 
15÷6  =  2
...
 Subtract  the  mean  value  from  each  of  the  measured  values  (x-­‐x’):  This  gives;  
1
...
5,  -­‐0
...
5,  2
...
5  
3
...
25,  2
...
25,  0
...
25,  6
...
 Add  all  the  squared  numbers  together:  ∑(𝑥 − 𝑥 / )0  =  17
...
 Divide  this  by  one  less  than  the  total  number  of  measurements:  
(1
...
5  

6
...
917  =  1

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