Module 4 : Section 3 - Variation Flashcards
Define variation
The differences that exist between individuals
Variation can occur ….
- within species
- between species
What is meant by variation within species
- Variation within a species is called intraspecific variation
- e.g. European robins weigh between 16g to 22g and show some variation in many other characteristics including length, wingspan, colour and beak size
What is meant by variation between species
- the variation between different species is called interspecific variation
- e.g. the lightest species of bird is the bee hummingbird, which weighs around 1.6 on average. The heaviest species of bird is the ostrich which can weigh up to 160kg
Varaition can be….
- continuous
- discontinuous
What is continuous variation
- When the individuals in a population vary within a range
- there are no distinct categories
- e.g. humans can be any height within a range (139cm, 175cm, 185.9cm, etc), not just tall or short
Give examples of continuous variation in animals
- Milk yield, e.g. cows can be produce any volume of milk within a range
- Mass, e.g. humans can be any mass within a range
Give examples of continuous variation in plants
- Number of leaves, e.g, a tree can have any number of leaves within a range
- Mass, e.g. the mass of the seeds from a flower head varies within a range
Give examples of continuous variation in microorganisms
- Width - e.g. the width of E. coli bacteria varies within a range
- Length - e.g. the length of the flagellum can vary within a range
What is discontinuous variation
- discontinuous variation is when there are two or more distinct categories
- each individual falls into only one of these categories, there are no intermediates
Give examples of discontinuous variation in animals
- Blood group, A, B, AB or O
Give examples of discontinuous variation in plants
- colour, e.g. courgettes are either yellow, dark green or light green
- seed shape, e.g. some pea plants have smooth seeds and some have wrinkled seeds
Give examples of discontinuous variation in microorganism
- Antibiotic resistance, e.g. bacteria are either resistant or not
- pigment production, e.g. some types of bacteria can produce a coloured pigment, some can’t
What can variation be caused by
- Genes
- the environment
- or both
What does genetic factors in causing variation referring to
- Different species have different genes
- individuals of the same species have the same genes but different versions of them (alleles)
- the genes and alleles an organism has make up its genotype
- the differences in genotype result in variation in phenotype
- examples of variation caused by only genetic factors include blood group and antibiotic resistance in bacteria
- you inherit your genes from your parents. This means variation caused by genetic factors is inherited
What is phenotype
The characteristic displayed by an organisation
What does environmental factors in causing variation refer to
- variation can also be caused by differences in the environment e.g. climate, food, lifestyle
- characteristics controlled by environmental factors can change over an organisms life
- examples of variation caused only by environmental factors include accents and whether people have pierced ears
What does genetic factors and environmental factors causing variation refer to
Genetic factors determine the characteristics an organism’s born with, but environmental factors can influence how some characteristics develop for example:
- height, genes determine how tall an organism can grow. But diet and nutrient availability affect how tall an organism actually grow
- flagellum, genes determine if a microorganism can grow a flagellum, but some will only start to grow them in certain environments e.g. if metal ions are present
How do you investigate variation
- usually you take samples of a population
- the mean is an average of the values collected in a sample
- it can be used to tell if there is variation between samples
Give an example that can be used to tell if there is variation between samples
The mean height of a species of tree in:
Woodland A = 26m
Woodland B = 32m
Woodland C = 35m
So the mean height varies
What is normal distribution
A normal distribution is symmetrical about the mean. Most samples will include values either side of the mean so you end up with a bell-shaped graph
What do you use to tell you about variation within a sample
Standard deviation
What is standard deviation
The standard deviation tells you how much the values in a single sample vary. It’s a measure of the spread of values about the mean
Sometimes you’ll see the mean written as e.g. 9_+_3. What does this mean
This means that the mean is 9 and the standard deviation is 3, so the most of the values are spread between 6 and 12
What does a large standard deviation mean
It means the values in the sample vary a lot
What does a small standard deviation mean
It tells that most of the sample data is around the mean value, so varies a little
