Topic 7 - Evolution Flashcards
What is genetic variation?
The differences in the alleles of jeans between members of the same species. It arises from a combination of genetic and environmental factors.
What are the three sources of genetic variation?
- Random fertilisation
- Meiosis
- Mutation.
What is random fertilisation?
During sexual reproduction gametes with different alleles combine randomly producing offspring with unique combinations of alleles.
How does meiosis result in genetic variation?
Independent assortment: homologous chromosomes during meiosis means alleles are distributed randomly into gametes.
Crossing over: between homologous chromosomes creates new combinations of alleles.
What is a mutation?
Changes in the DNA base sequence of a can lead to the formation of new alleles.
These mutations can be inherited if they occur in gametes, contributing to genetic variation in the next generation.
What is natural selection?
Species evolve an adapt to their environment driven by variation competition and inheritance of advantageous traits.
What is a niche?
- A species role within the environment including how it obtain resources and interacts with other species.
What happens to species with overlapping niches?
- species with overlapping niches compete with one another. The better adapted species out compete others surviving and reproducing.
What is intraspecific competition?
Competition within a species occurs due to limited resources.
What is inter-specific competition?
Competition between species occurs due to limited resources.
What is meant by survival of the fittest?
- individuals with advantageous alleles are better suited to their environment, survive longer and reproduce successfully.
- Variation in genotypes and phenotypes increases a populations ability to adapt to environmental changes.
What is the process of natural selection?
- A population shows phenotypic variation due to genetic differences.
- Environmental change: a change occurs altering the selection pressure.
- Selective advantage: some individuals possess add advantages alleles that improve survival and reproduction.
- Reproduction: these individuals survive, reproduce and pass advantageous alleles to their offspring.
- Evolution: over generations allele frequency shift in the population favouring traits that improves survival in the current environment.
What is a common example of natural selection?
Antibiotic resistance in bacteria:
- Some bacteria possess a mutation that allows them to survive antibiotics.
- These bacteria have a selective advantage and reproduce, passing on the resistant allele.
- Overtime, the frequency of the resistance increases, resulting in an evolved population resistant to antibiotics.
What is directional selection?
- occurs when the environmental conditions change.
- Individuals with phenotypes better suited to the new environment are more likely to survive reproduce and pass on their advantages alleles
- Overtime the phenotype shifts in the direction of the advantages traits.
What is stabilising selection?
- occurs in stable environments
- Individuals with phenotypes closest to the mean are more likely to survive and reproduce.
- Extremes of the phenotype are selected against reducing diversity within the population.
What is disruptive selection?
- favours extreme phenotypes at both ends of the distribution selecting against the mean.
- Leads to increased genetic diversity and may result in the formation of two distinct groups
What is meant by evolution?
The gradual change in allele frequency within a population overtime driven by natural selection.
What are the three pieces of evidence that evolution?
- Molecular evidence.
- Fossil record.
- Homologous structures.
How does a fossil record show evidence for evolution?
- Shows how species have changed over millions of years
- Provide things between extinct and modern species
How does molecular evidence show evidence for evolution?
- similarities in DNA sequences amino acid sequences and protein structures suggest common ancestry.
How does homologous structures show evidence for evolution
Structures with similar anatomy but adapted for different purposes.
What is reproductive separation?
The process that leads to the formation of a new species when populations of the same species become genetically isolated. Overtime this isolation prevent individuals from different populations from interbreeding successfully.
What is Allopatric speciation?
When a species become geographically isolated by mountain ranges or rivers causing them to adapt to their new environment which will be slightly different and therefore they cannot successfully reproduce together meaning they are different species.
What is sympatric isolation?
When a species become reproductively isolated due to behaviour isolation such as changes in courtship behaviour or temporal isolation such as species reproducing a different times.
What are the three stages of reproductive separation?
- Isolation of populations.
- Accumulation of genetic differences.
- Formation of a new species.
What is the accumulation of genetic differences stage in reproductive separation?
- once a species is isolated populations experience different mutations and undergo natural selection based on their unique environments.
- Genetic drift also especially in small populations.
How does reproductive separation form a new species?
-Overtime the genetic differences become so significantly that the population can no longer interbreed to produce fertile offspring.
What is speciation?
When new species arise when populations become reproductively isolated and can no longer reproduce successfully.
Explain Allopatric speciation [5 marks]
- Occurs due to geographical isolation of mountain ranges and rivers or continental drift.
- Gene flow between separated populations is reduced.
- Each population experiences different selection pressures.
- Overtime the population accumulate genetic differences through mutation and natural selection..
- Eventually, they become so genetically distinct they cannot reproduce offspring
Explain sympatric speciation
- occurs within the same geographical area
- Caused by reproductive isolation
- mutations: chromosomal changes can result in individuals being unable to breed with the original population
- behavioural isolation changes in courtship behaviour may prevent recognition between individuals
- anatomical isolation: structural differences e.g. compatibility of reproductive organs can prevent successful mating
What is the bottleneck effect?
- The population bottleneck occurs when a population size is drastically reduced due to natural disaster disease or human activity.
- The remaining population may have reduced genetic diversity different allele frequencies compared to the origional population
