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Evolution may lead to speciation (Natural selection (Tips for NATURAL…
Evolution may lead to speciation
Factors which cause variation in phenotypes
Changes in the environment
Formation of a lake
Flooding
Drought or extreme heat
Seasons (Spring, Summer, Autumn, Winter)
Genetic variation (Mutations)
Deletion: either a base or group of bases are removed completely from the base sequence.
Substitution: Either 1 or a group of bases are removed from the base sequence and replaced with a different set of bases
Inversion: A group of bases are inverted so that they are the mirror image of themselves
Addition: Where either 1 or a group of bases are added to the base sequence
Duplication: Where 1 or a group of bases are duplicated in the base sequence
Translocation: Where either 1 or a group of bases are moved onto a different chromosome swapping either with the group or base
Types of variation
Discontinuous variation
A phenotype that is controlled by a single gene can be described as discontinuous or categorical data
This type of variation is genetic only and phentypes fit into discrete categories eg. Blood
Data should be displayed in a bar chart
Continuous variation
A phenotype which produces no discrete catergories is heavily influenced by environmental factors is also controlled by genes
Ther data could take any value in a range eg. Mass and height and is known as continuous data
This type of data is usually displayed as a histogram
In most cases variation is caused by both genetic and environmental influences
Natural selection
Predation, disease and competition for the means of survival result in differential survival and reproduction
Every organism is subjected to the process of selection based on its suitability to survive in the conditions that exist at that time
Environmental factors that limit the population of a species are called selection pressures. These include predation, disease and competition
Organisms with phenotypes providing selective advantages are likely to produce more offspring and pass on their favourable alleles to the next generation
Tips for NATURAL SELECTION EXAM QUESTIONS
M
utations
A
lleles/advantage
S
election pressure
S
urvive
D
ifferential
R
eproductive success
I
nherit alleles
F
requency increases
T
ime (many generations)
1) Some organisms already have an advantageous allele for X (apply to question ) due to mutation which gives them a selective advantage
2) The organism with the advantageous allele are more more likely to survive and reproduce to produce more offspring than organisms without the resistance allele
3) Some of the offspring of this organism will inherit the advantageous allele
4) Over many generations the allele frequency of the advantageous allele in the population will increase
5) Over time a greater proportion of the population will have the advantageous allele
Types of selection
Stabailing selection
Occurs in pulatons where the environment is stable
Selective pressure at both ends of distribution
The extreme phenotypes are not favoured and variability is reduced
Reduced opportunity for evolutionary.change (range of characteristic in a population
Eg. Birth mass in humans. If the baby is too light then the baby will die.If the baby I’d too heavy they are also likely to die
Directional selection
Environmental change may produce new selection pressure that favours an extreme phenotype
Some organisms will already posses the advantageous allele due to a random mutation allowing them to produce more offspring that will have the advantageous allele
Over time the extreme mutation will become the dominant allele in the population and the meanwill shift
Disruptive selection
Both of the extremes are favoured so the mean is selected against
Has no mean as there are 2 peaks on the representative data
An example could be fur length and temperature the hot temperatures in the Summer could lead to an animal developing short fur and hibernating in the winter. Organisms of the same species could also adapt to to have long fur in the Winter and hibernate during the summer which could lead to speciation