F212 3 Evolution Flashcards
(33 cards)
Interspecific Variation
Variation between species
Variation
The differences between individuals
Intraspecific Variation
Variation within a species
Continuous Variation
Definition
A whole range of types between two extremes
Controlled by genes and the environment
Most individuals are close to the mean, few individuals at the extremes
Discontinuous Variation
Definition
Distinct categories with no intermediate values
This type if variation is determined by one gene
Continuous Variation
Examples
Height in humans
Length if leaves on an oak tree
Length of stalk of a toadstool
Discontinuous Variation
Examples
Gender, mammals are either male or female, plants can be male, female or hermaphrodite
Some bacteria have flagella and others don’t
Human blood groups, A, B, AB, O
What Causes Variation?
Genetics
Environment
Genetic Causes of Variation
Mutations - a random change in the DNA base sequence amuses genetic variation between individuals
The combination of alleles offspring inherit from their parents determines their visible characteristics
Environmental Causes of Variation
Environmental factors do not change the genes that a person has, they affect the visible characteristics
E.g. A persons skin will tan and become darker in the sun
A plant will grow towards a source of light
Behavioural Adaptations
Definition
An aspect of the behaviour of an organism that helps it to survive in the conditions it lives in
Physiological / Biochemical Adaptions
Definition
An adaptation that ensures the correct functioning of cell processes
Anatomical Adaptations
Definition
Any structure that enhances the survival if the organism is an adaptation
Behavioural Adaptations
Example
When you touch an earth worm it contracts and withdraws into its burrow
This helps to avoid it being eaten
Physiological / Biochemical Adaptions
Example
Yeast produces the correct enzymes to respire the sugars in their current environment
Anatomical Adaptions
Example
Many bacteria have flagella which allow them to move independently
Darwin’s Observations
Variation between offspring
Offspring inherit features form parents
Organisms have the ability to produce large numbers of offspring
Populations of organisms remain relatively stable over time
Darwin’s Conclusions
The Theory of Evolution
Genetic variation between individuals
Over reproduction
Struggle to survive
Only the best adapted survive
Survivors reproduce passing on the advantageous genes
Gradual changes in the population over many years
Speciation
The formation of a new species
Allopatric Speciation
Speciation as a result of a geographical cause, two parts of a population become separated and evolve differently
Sympatric Speciation
Two species remain in the same geographical area but a reproductive barrier occurs e.g.
- a biochemical change preventing fertilisation
- behavioural change meaning a courtship dance is not recognised
- physical change in sexual organs
Selection Pressure
Definition
An environmental factor which determines which species survives
Evidence for the Theory of Evolution
Fossils
General trend in the fossil record shows smaller more simple organisms in the distant past and more complex organisms today
Darwin found fossils of Brachiopods which had slowly changed over time
Evidence for the Theory of Evolution
Problems with Fossils
Fossil evidence is incomplete
Usually on,y the hard parts of the organism survive to become a fossil
Fossils only form under certain conditions
Can be damaged or destroyed by the movements of rocks
