Unit 5 - Evolution May Lead To Speciation Flashcards
Definition of phenotype?
The expression of the genetic constitution and their interaction with the environment.
What can lead to genetic variation?
-environmental factors
-mutations
-meiosis
-random fertilisation of gametes
What is discontinuous variation?
Where variation is due to genetics only, phenotypes fit into discrete categories. A phenotype like this is controlled by a single gene.
The environment has very little influence.
How is discontinuous variation normally displayed?
As a bar chart.
What is continuous variation?
Continuous variation is when the characteristics can take any value. It results from many different genes, polygenic.
Environmental factors also have a large impact.
How can continuous variation be represented?
As a histogram.
What are selection pressures?
Environmental factors that limit the population of a species. These also include predation, disease and speciation.
How to answer natural selection exam questions?
1) Due to a mutation some organisms have an advantageous allele for C(name the allele), which gives them a selective advantage in the presence of the selection pressure (name it).
2) The organisms with the advantageous allele are most likely to survive and reproduce, than organisms without the 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 increases.
5) Name the type of selection (directional, disruptive, stabilising)
MASSRIFT?
M-mutations
A-alleles/advantage
S-selection pressure/selection advantage
S-survive
R-reproduce
I-inherit allele
F-frequency increases
T-type of selection
What is stabilising selection?
-Occurs in all populations where environment is stable.
-Selective pressure at both ends of distribution.
-The intermediate phenotype is selected for.
-The extreme phenotypes are selected against.
-Reduces variability, the size of the range within the population.
-Reduces opportunity for evolutionary change.
-Reduces the range of possible characteristics in the population.
What is directional selection?
-Mean in population represents optimum for existing conditions.
-Environmental change may produce new selection pressure that favours an extreme phenotype.
-When conditions change, phenotypes necessary for survival also change.
-Some organisms, due to mutation, will possess an allele which gives them an advantage in the new environment.
-Those with the favourable allele will be selected for.
-Those that don’t have the favourable allele will be selected against.
-Over time selection means these will predominate and the mean will shift.
What is disruptive selection?
-Both extremes of the phenotype are selected for.
-The intermediate mean is selected against.
-Could lead to speciation - one species has long fur and is active in winter, the other short fur and active in summer.
Definition of gene pool?
All the alleles in a population.
Definition of speciation?
The development of new species from an existing species. It occurs when populations of the same species have separate gene pools, so they cannot interbreed to produce fertile offspring.
What is allopatric speciation?
1) 2 populations of the same species become geographically isolated (use the Q)
2) This is allopatric speciation
3) They cannot interbreed, forming separate gene pools
4) The 2 areas may have different selection pressures (different abiotic conditions)
5) Within each population mutations have already formed advantageous alleles to the selection pressures
6) Individuals with the advantageous alleles survive and reproduce forming more offspring
7) The offspring inherit these alleles increasing the allele frequency over many generations
8) This causes disruptive selection between the 2 populations
9) After a long period of time, the populations cannot interbreed to produce fertile offspring.
