3. Evolution

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Define 'Variation'
Presence of differences between individuals, without variation evolution wouldn't occur.
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Continuous variation
Full range of intermediate phenotypes between two extremes. Quantitative. Normal distribution pattern. Largely affected by genes, environment.
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Examples of continuous variation
Height, weight, length, no of leaves, milk yield
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Discontinuous variation
Two or more distinct categories of phenotypes, no set pattern
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Examples of discontinuous variation
Blood type, sex, eye colour, presence of flagella
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Causes of variation
Weight for example, metabolism determined by GENES and nutrition determined by LIFESTYLE/ENVIRONMENT
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Define 'Adaptation'
A feature that enhances an individual's chance of survival and long term reproductive success
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Types of adaptation (Anatomical)
Structural features which enhances chance of survival (streamlined shape, blubber)
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Types of adaptation (Behavioural)
Responses an organism makes to its environment (play dead, stomata open in day)
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Types of adaptation (Physiological/Biochemical)
Processes inside the body that increases chance of survival (hibernation lowers metabolism)
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Define 'Selection pressure'
An external pressure that drives evolution in a particular direction
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What happens to those better adapted to the selection pressure?
They survive and pass on these desired characteristics to their offspring and perhaps the next generation
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What were Darwin's 4 observations?
1. Offspring appear genetically similar to their parents 2. No two individuals are identical 3. Organisms have the ability to produce large numbers of offspring 4. Populations in nature tend to remain fairly stable in size
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What conclusions can you make from Darwin's observations?
- There is a struggle to survive - Better adapted individuals survive and pass those characteristics to their offspring - This can lead to the formation of new species
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Define 'Speciation'
Formation of a new species from a pre-existing one
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What is a reproductive barrier?
Individuals from the same population getting seperated
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What makes a new species?
- Separated species (THE SPECIES HAVE VARIATION OTHERWISE WITH SELCTION PRESSURE THEY WOULD ALL SURVIVE OR ALL DIE) - Populations change to adapt to their environment - Acquire genetic changes - Over time they are no longer genetically compatible
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Types of speciation
Geographical separation leads to Allopatric speciation. Reproductive barriers (biochemical change) leads to Sympatric speciation (mutation).
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Evidence for evolution (fossils)
Gradual change over time, deeper down crust older the fossils get
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Disadvantages of using fossils as evidence
Soft tissue not preserved, special conditions needed for fossils to form
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Evidence for evolution (DNA, RNA)
Comparison of biological molecules, similarity in sequences indications similarity in species, Cytochrome C, DNA/RNA polymerase
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SUGGEST
Variation (mutation, gene combinations) --> Selection pressure (struggle for survival) --> Adapted individuals survive and reproduce --> Greater proportion of adapted individuals in next generation
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Card 2

Front

Continuous variation

Back

Full range of intermediate phenotypes between two extremes. Quantitative. Normal distribution pattern. Largely affected by genes, environment.

Card 3

Front

Examples of continuous variation

Back

Preview of the front of card 3

Card 4

Front

Discontinuous variation

Back

Preview of the front of card 4

Card 5

Front

Examples of discontinuous variation

Back

Preview of the front of card 5
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