A-level Biology - 3.3.8 Evolution may lead to Speciation
Evolution is the process by which allele frequencies in a population change over generations. These genetic changes can lead to variations in traits, allowing populations to adapt to their environment over time.
What is evolution?
Is the change in allele frequencies in a population over time
Key Terms
What is evolution?
Is the change in allele frequencies in a population over time
Name 2 methods in which evolution occurs
Natural selection
Genetic drift
Describe how natural selection occurs by evolution
Selection pressures (e.g. predation, disease, competition) create struggle for survival
Genetic variation between individuals
Individua...
Name 4 observations Darwin made
Population remain stable
Offspring appear similar to their parents
No two individuals are the same
Organisms have the ability to ...
What type of variation results in evolution?
Only genetic variation
What is a selection pressure?
Anything that affects an organism’s chance of survival and reproduction
Related Flashcard Decks
Study Tips
- Press F to enter focus mode for distraction-free studying
- Review cards regularly to improve retention
- Try to recall the answer before flipping the card
- Share this deck with friends to study together
| Term | Definition |
|---|---|
What is evolution? | Is the change in allele frequencies in a population over time |
Name 2 methods in which evolution occurs | Natural selection Genetic drift |
Describe how natural selection occurs by evolution | Selection pressures (e.g. predation, disease, competition) create struggle for survival Genetic variation between individuals Individuals with (beneficial) allele that makes them better adapted to selection pressure than others This increases their chance of survival & more likely to reproduce and pass on this (beneficial) allele Increased freqency of beneficial alleles in next generation Offspring more likely to survive, reproduce and pass on their alleles ∴ frequency of beneficial alleles in gene pool increases from generation to generation |
Name 4 observations Darwin made | Population remain stable Offspring appear similar to their parents No two individuals are the same Organisms have the ability to reproduce |
What type of variation results in evolution? | Only genetic variation |
What is a selection pressure? | Anything that affects an organism’s chance of survival and reproduction |
Name 3 selection pressures | Human activity / pollution Availability food sources Diseases Competition Predators Land clearance |
Types of natural selection affect ____ ______ in different ways | allele frequency |
Name the 3 types of natural selection | Stablising Selection Directional Selection Disruptive Selection |
Define Stablising Selection | Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce (Favours the average = averages increase and extremes decrease) |
When does stablising selection occur? | Occurs when environment isn’t changing = reduces range of possible phenotypes |
Define Directional Selection | Where individuals with alleles for single extreme phenotype are more likely to survive and reproduce |
When does directional selection occur? | Occurs in response to environmental change |
Describe Disruptive Selection | Where individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce |
When does speciation occur? | When populations of same species become reproductively isolated |
Name the 2 types of speciation | Allopatric Speciation Sympatric Speciation |
What does allopatric speciation involve? | Geographical isolation |
Describe allopatric speciation (6x) | Populations that are geographically separated will experience slightly environmental different conditions Populations will experience different selection pressures ∴ = selection for different alleles Variation due to mutation Selection for advantageous allele = selected organisms survive and reproduce Leads to changes in allele frequency Eventually, individuals from different populations changed so much = can’t breed to produce fertile offspring Become reproductively isolate |
Allopatric Speciation Name 3 ways in which different changes in allele frequencies could occur | Different alleles could be more favourable in new conditions and directional selection could take place e.g. colder climate: directional selection will act on alleles for fur length = increasing frequency of allele for longer fur length Mutations could occur in each population Genetic drift |
What is sympatric speciation caused by? | Mutations, changes in mating patterns |
Describe how sympatric speciation could occur due to mutations | Most eukaryotic organisms = diploid Sometimes mutations occur that increase no. of chromosomes Known as polyploidy Individuals with different no. of chromosomes can’t reproduce sexually to give fertile offspring e.g. polyploid organism in diploid population = reproductively isolated If polyploid organism reproduces asexually = new species develops |
Sympatric speciation is more common in ____ than ______ | plants than animals |
Why does reproductive isolation occur? | Occurs ∵ changes in alleles and phenotypes in some individuals prevent breeding successfully with individuals without these changes |
Name 3 examples of changes that occur to individuals that leads to reproductive isolation | Seasonal Different flowering or mating seasons Or become sexually active at different times of year Mechanical Changes in genitalia prevent successful mating Behavioural Develop courtship rituals that aren’t attractive to main populations |
What is genetic drift? | When chance rather than environmental factors dictates which individuals survive, breed and pass on their alleles |
Give an example of how genetic drift could lead to speciation | Individuals within population show variation in their genotypes By chance, allele for one genotypes (B) is passed on to offspring more often than others ∴ no. of individuals with the allele increases Changes in allele frequency in 2 isolated populations could eventually lead to reproductive isolation and speciation |
Evolution by genetic drift has greater effect in ____ populations | smaller |
Why does genetic drift have a greater effect in smaller populations? | ∵ chance has greater influence in smaller populations (In larger populations, any chance variations in allele frequency tend to even out across whole population) |
Explain how an insect population can become resistant to an insectidice (3) | mutations producing alleles giving resistance natural selection / leads to increased frequency of alleles in population |
Copper-tolerant grass produces its flowers eariler in the year than non-tolerant grass of the same species. Explain how this might produce two different species of grass. (5) | (populations are) reproductively isolated (due to different flowering times) ∴ no flow of alleles between the populations/different (random) mutations in each group different selection pressures frequency of alleles will change (genetic differences lead to) members of populations become unable to interbreed and produce fertile offspring |
One farmer stated that the increase in the use of Bt crop plants had caused a mutation in one of the insect species and that this mutation had spread to other species of insect. Was he correct? Explain your answer. (4) | Mutations are random Only the rate of mutation is affected by environment Different species do not interbreed / do not produce fertile offspring So mutation/allele cannot be passed from one species to another |
There was a time lag between the introduction of Bt crops and the appearance of the first insect species that was resistant to the Bt toxin. Explain why there was a time lag. (3) | Initially one insect with favourable mutation / allele; Individuals with (favourable) mutation / allele will have more offspring Takes many generations for (favourable) mutation / allele to become the most common allel |