Natural selection and speciation Flashcards
Genetic and environmental factors cause ….
Variation
What is the primary source of genetic variation?
Mutation
Define gene pool
All of the alleles of all of the genes of all the individuals within a particular population at a given time
What is intraspecific competition?
Competition between individuals of the same species
Give 3 reasons why differential survival and reproduction could occur.
Predation
Disease
Competition
An organism has a selecive advantage. What does this mean?
Better adapted for the conditions present.
More likely to survive and reproduce.
Pass on favourable alleles
How is genetic variation produced?
Crossing over
Independent segregation/random assortment
Random fusion of gametes
Mutation
Name 3 types of selection
Stabilising
Directional
Disruptive
Describe stabilising selection
Preserves the average phenotype
Selection against extreme phenotypes.
Occurs when environment is stable
Give an example of stabilising selection
Human birth weight
Give an example of directional selection
Antibiotic resistance in bacteria
Give a defition of speciation
Evolution of a new species from an existing one
Define a species
Group of similar organisms that breed producing fertile offspring
Give the 2 types of speciation
Allopatric and sympatric
Allopatric speciation occurs when …..
When 2 populations become geographically isolated
Give examples of how organisms might be geographical isolated
Physical barrier which prevents interbreeding e.g. oceans, rivers, mountains, deserts, landslide
Define reproductive separation
when 2 populations can no longer interbreed and produce fertile offspring
Example of allopatric speciation
Finches on the Galapagos Islands!
Sympatric speciation occurs
Within a population of organisms living in the same area (doesn’t require geographical isolation)
Sympatric speciation arises because ….
They have different breeding seasons
They may inhabit different habitats in the same area so never meet, Anatomical differences,
Name the type of selection shown
stabilising
Name the type of selection shown
directional
Describe how allopatric speciation occurs
Two populations are geographically isolated
Creates separate gene pools with no interbreeding
Variation due to mutation
Different selection pressures
Differential reproductive success
Leeds to change in allele frequencies
Occurs over long period of time
Populations no longer able to interbreed to produce fertile offspring
Name the type of selection shown
Disruptive
What does evolution do to the frequency of alleles in a population?
Changes them - increase or decrease
What happens to the frequency of the alleles that give organisms an advantage?
Increases
What happens to those organisms that are better adapted to the selective pressures in the environment?
Survive, reproduce and pass on favourable alleles
What happens to the phenotype during stabilising selection?
Preserves the middle of the range phenotypes
Which phenotype is selected for during directional selection?
An extreme phenotype - these are more likely to survive and reproduce
What phenotype is preferred in disruptive selection?
BOTH extremes (select against the middle phenotype)
What is genetic drift?
Chance (not the environment) determines which organisms survive,
reproduce and pass on their alleles
Genetic drift has a greater effect on which size population?
Smaller populations
Describe Sympatric Speciation
Occurs in the same population
Mutations cause variation in alleles
Reproductive separation with no gene flow
Different alleles selected for
Change in allele frequency
Disruptive selection
Different species formed which cannot interbreed
