Topic 7B: Population and Evolution Flashcards
What is a species?
a group of similar organisms that produce 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 a gene pool?
Complete range of alleles present in the population
What is allele frequency?
How often an allele occurs in a population
What does the Hardy-Weinberg principle predict?
that the frequency of alleles in a population wont change from one generation to the next
The Hardy-Weinberg prediction is only true under what conditions?
- large population
- no immigration/emigration
- no mutations
- no natural selection
- random mating
What do the Hardy-Weinberg equations calculate?
-frequency of alleles
What is the equation that calculates allele frequency?
p + q = 1
What is the equation that calculates genotype/phenotype frequency?
p^2 + q^2 + 2pq = 1
p is….
dominant
q is….
recessive
What is variation?
differences that exist between individuals
What causes variation?
- genes
- the environment
- or both
Variation within species means….
wide range of different phenotypes
Although individuals of the same species have the same genes but
- they have different alleles
- this causes genetic variation
What is the main source of genetic variation?
-mutation BUT also -crossing over -independent segregation -random fertilisation
What type of variation is caused within species most commonly?
a combination of genetic and environmental factors
Only genetic variation causes….
evolution
What is evolution?
A change in allele frequencies over time
What is a method by which evolution occurs?
Natural selection
Outline how evolution changes the allele frequency…
- Individuals of the same species vary between different alleles
- selection pressures create a struggle for survival
- organisms better adapted to the selection pressure survive/reproduce/pass onto offspring
- greater proportion inherit the beneficial alleles
- changes the frequency of alleles
Name the three different types of selections?
- Directional
- Stabilising
- Disruptive
What is stabilising selection?
- favours the middle of the range
- environment isnt changing
- reduces the range of possible phenotypes
- avoid extremes
What is directional selections
- favours an extreme phenotype
- response to environmental change
What is disruptive selection?
- favour BOTH extreme phenotypes
- opposite to stabilising selection
- middle range is lost
- environment favours more than one phenotype
Explain an example of stabilising selection
- fur length
- fur at extremes reduced the chance of survival
- because harder to maintain body temperature
- so average fur length are most likely to survive and reproduce
Explain an example of directional selection
- cheetahs run really fast
- due to directional selection
- individuals with increased speed more likely to catch prey
- these compete with slower individuals and survive and reproduce etc
Explain an example of disruptive selection
- range of beak sizes
- birds with large beaks are designed to eat large seeds
- birds with small beaks are designed to eat small seeds
- birds with medium sized beaks have reduce chance of survival
- pop of small and large beaks increases
Name two types of speciation?
- Allopatric
- Sympatric
What is speciation?
development of new species from an existing one
How does speciation occur?
when population of the same species becomes reproductively isolated
What does it mean being reproductively isolated?
when the species can no longer interbreed to produce fertile offspring
What is reproductive isolation?
changes in allele frequency cause changes in the phenotypes
What does geographical isolation lead to?
allopatric speciations
Outline allopatric speciations
- population geographically isolated due to selection pressure OR genetic variation due to mutation
- creates physical barrier
- pop experience different selection pressures
- different environmental conditions
- changes in the alleles cause directional selection
- causes differential reproductive success
- changes in allele frequency/gene pool
- they become reproductively isolated
Examples of selection pressures
predatation, climate, disease
What is sympatric speciation?
Random mutations that could occur within population, preventing members of that population breeding with other member of the species
What is polyploidy?
When mutations can occur that increase the number of chromosomes
Example of sympatric speciation?
- eukaryotic organisms are diploid
- if they are polyploidy then reproduction can not happen sexually
- polyploidy organism becomes reproductively isolated
- if polyploidy organisms can reproduce asexually they new species could develop
Is sympatric speciation more common in plants or animals?
Plants
What in are the ways species can be reproductively isolated?
Changes in:
seasonal
mechanical
behavioural
What is a seasonal change?
-developing different flowering/mating seasons
OR
-becoming sexually active at different times of the year
What is a mechanical change?
changes in the genitalia preventing successful mating
What is a behaviour change?
a group of individuals developing courtship rituals that are not attractive to the main population
What is genetic drift?
When chance rather than environment factors dictates which individuals survive breed and pass on their alleles.
Example of genetic drift
- variation in genotype
- by chance allele for one genoptype is passed on to offspring
- allele frequency of that allele increases
- reproductive isolation
Evolution can occur by
- genetic drift
- natural selection
When does genetic drift have a greater effect?
- When population size is smaller and so chance has a greater influence
- in greater population the chance variation tends to even out
Evolutionary changes causes..
greater diversity
