Chapter 18 - Populations and evolution Flashcards
What is the gene pool?
All the allele of all the genes of a population
What is allelic frequency?
The number of times an allele occurs within the gene pool
What will the allelic frequency always be?
Less than one
What does the Hardy-Weinberg principle predict?
The frequency of alleles will stay constant over generations providing there are no mutations
What are the five conditions required for the Hardy-Weinberg principle to work?
No mutations Population is isolated - no new alleles No selection Large population Mating is random
What does p equal?
Dominant allele
What does q equal?
Recessive allele
What are the two Hardy-Weinberg equations?
p + q = 1
p^2 + q^2 + 2pq = 1
What are the three ways in which variation occurs?
Mutations, meiosis, random fertilisation of gametes
How does meiosis produce variation?
Nuclear division produces new combinations of alleles
What does stabilising selection do?
Preserves the average phenotype by reducing the variation of values around the mode
What does directional selection do?
Favours an extreme phenotype
What does disruptive selection do?
Favours both extreme phenotypes
How does directional selection occur?
Natural selection
What may disruptive selection result in?
Speciation
How does disruptive selection occur?
There are two environments and a different characteristic is advantageous in each
Are environmental factors usually controlled by a single gene?
No - normally it is many
What will we get if we plot an environmental factor on a graph?
Bell shaped normal distribution curve
Where variation is largely due to genetic factors, how can this information be represented?
On a bar chart or line graph
Are genetic factors usually controlled by a single gene?
Yes
What are selection pressures?
The environmental factors limiting the population of a species
What is a gene pool?
The total number of alleles within a population
Why have species evolved to have high reproductive rates?
To ensure there is a sufficiently large next generation
How do large reproductive rates contribute to natural selection?
When there are too many individuals for the environment to support, infraspecific competition occurs which ensure the best adapted survive and the worst adapted die
Why is variation important?
To adapt to changing conditions
What impact does environment have on allelic frequency?
Impacts the frequency of a mutant allele that is already in the gene pool
What is speciation?
The evolution of a new species from an existing one
What is adaptive radiation?
Population separates
Mutations occur, forming new alleles
Each environment is slightly different - different selection pressures
Natural selection leads to changes in allelic frequency
What is genetic drift?
In small populations, there is a smaller gene pool
As there are so few alleles, there is an uneven chance of each being passed on
Once passed on, a high frequency means the whole population is impacted quickly
Population changes rapidly - more likely to form new species
What are the two types of speciation?
Allopatric and sympatric
What is allopatric speciation?
A species is geographically separated There are different environments Mutations = new alleles Different selection pressures Different alleles become advantageous Natural selection occurs New species formed
Which type of speciation involves geographical isolation?
Allopatric
Example of allopatric speciation
Galapagos finch
What is sympatric speciation?
A species is separated in some way other than geographic separation
Examples of ways species can be separated
Geographical
Ecological
Mechanical
Temporal
