7B populations and evolution Flashcards
What is a species?
A group of organisms that can reproduce to give fertile offspring
What is a population?
A group of organisms of the same species living in a particular area at a particular time
What is allele frequency?
How often an allele occurs in a population
What does the Hardy-Weinberg principle predict?
That the frequiencies of alleles in a population won’t change from one generation to the next
What does the Hardy-Weinberg principle depend on?
Large population size
No mutations
No natural selection
No immigration or emigration
Needs to be random mating
p + q = 1
p is the dominant allele
q is the recessive allele
p2 +2pq + q2 = 1
p2 = the frequency of the homozygous dominant
2pq = the frequency of the heterozygous genotype
q2 = the frequency of the homozygous recessive
What is intraspecific variation?
Variation within a species meaning individuals show a wide range of phenotypes
Variation is the differences that exist between individuals
Most variation is caused by a combination of genetic and environmental factors but only genetic variation results in evolution
What are sources of variation?
Mutation
Independent segregation
Crossing over
Random ferilisation
How does natural selection work?
Individuals of the same species vary because they have different alleles
Predation, disease and competition are selection pressure which create a struggle for survival
Some individuals are better adapted to selection pressures
So different levels of survival and reproductive success in a population
Individuals with a phenotype that increases their chance of survival are more likely to survive, reproduce and pass on their beneficial alleles to their offspring
A greater proportion of the next generation inherit beneficial alleles
So the frequency of the beneficial alleles in the gene pool increases from generation to generation
What is disruptive selection?
Where individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce
It occurs when the environment favours more than one phenotype
What is speciation?
The development of a new species from an existing species
When does speciation occur?
When populations of the same species become reproductively isolated
Changes in the allele frequency causes changes in the phenotype which means they can no longer interbreed to produce fertile offspring
What is allopatric speciation?
Requires geographical isolation
Changes in allele frequency lead to differences in the gene pool of each population
Populations become reproductively isolated
So the two populations will become separate species
What is sympatric speciation?
Where a population doesn’t have to become geographically isolated to become reproductively isolated
Due to random mutations
