Evolution and Speciation Flashcards
What causes phenotypic variation?
- Genetic variation
- Environment
What is the primary cause of genetic variation?
Mutation
How do mutations cause genetic variation?
Mutation results in the generation of new alleles.
- The new allele may be advantageous, disadvantageous or have no apparent effect on phenotype
- New alleles are not always seen in the individual that they first occur in
- They can remain hidden within a population for several generations before they contribute to phenotypic variation
What are other causes of genetic variation?
- Crossing over of non-sister chromatids during prophase I of meiosis
- Independent assortment of homologous chromosomes during metaphase I of meiosis
- Random fusion of gametes during fertilisation
How does crossing over cause genetic variation?
It can result in a new combination of alleles on the two chromosomes. (Genetic variation between gametes produced by an individual)
How does independent assortment cause genetic variation?
Causes different combinations of chromosomes in daughter cells. (Genetic variation between gametes produced by an individual)
How does random fertilisation cause genetic variation?
Each gamete carries substantially different alleles. (Genetic variation between zygotes and resulting individuals)
What is natural selection?
The process by which individuals with a fitter phenotype are more likely to survive and pass on their alleles to their offspring so that the advantageous alleles increase in frequency over time and generations.
What is genetic drift?
A gradual change in allele frequencies in a small population due to chance and not natural selection.
What does selective advantage result in?
- Individuals with phenotypes providing selective advantages are likely to produce more offspring and pass on their favourable alleles to the next generation
- Over time, this differential reproductive success has an effect on the allele frequencies within a gene pool
- Alleles that are favourable will increase in frequency in a gene pool
- Alleles that are not favourable will decrease in frequency in a gene pool
What are the types of selection?
- directional
- stabilising
- disruptive
Describe disruptive selection.
Natural selection that maintains high frequencies of two different sets of alleles.
What is evolution?
The formation of new species from pre-existing species over time, as a result of changes to gene pools and allele frequencies from generation to generation.
What changes can lead to reproductive separation?
Seasonal changes - some individuals in a population may develop different mating or flowering seasons to the rest of the population
Mechanical changes - some individuals in a population may develop changes in their genitalia that prevent them from mating successfully with individuals of the opposite sex
Behavioural changes - some individuals in a population may develop changes in their courtship behaviours, meaning they can no longer attract individuals of the opposite sex for mating
What are the types of speciation?
- Allopatric
- Sympatric
Describe allopatric speciation.
- Allopatric speciation occurs as a result of geographical isolation due to geographical barriers. These may be natural (e.g. lake or mountain range), or man-made (e.g. motorway)
- This creates two populations of the same species who are reproductively separated from each other, and as a result, no genetic exchange can occur between them
- If there are sufficient selection pressures acting to change the gene pools within both populations then eventually these populations will diverge and form separate species
- The changes in the alleles/genes of each population will affect the phenotypes present in both populations
- Over time, the two populations may begin to differ physiologically, behaviourally and morphologically
Describe sympatric speciation.
- Sympatric speciation takes place with no geographical barrier
- A group of the same species could be living in the same place but in order for speciation to take place there must exist two populations within that group and no gene flow occurs between them
- Therefore, something has to happen that splits or separates the two populations:
- Ecological separation: Populations are separated because they live in different environments within the same area
- Behavioural separation: Populations are separated because they have different behaviours
Explain how speciation can occur due to geographical barriers?
1) Geographic isolation / allopatric
2) Reproductive separation
3) Different selection pressures
4) Random advantageous mutation
5) Alleles are passed on over many generations
6) Allele frequency increases
7) Eventually, the 2 populations can no longer interbreed
features of licen/ saprobionts
- 2 different species co existing
- made up of algae: : can photosynthesise so creating glucose, carbohydrates which it shares w fungus
- made up of fungus: can absorb water and release extracellular enzymes onto rock which can break down rock to release minerals
- meaning theyre able to survive even though:
- little water available
- no food source
- no minerals
