Evolution Flashcards
What is evolution
A change in inherited characteristics of a group of organisms over time
What is evolution in alleles
-A change in allele frequency over time
What is stabilising selection
- Occurs when environment stays unchanged
- Favours the intermediate phenotype types (increase in ‘average’ alleles than reduction in ‘extreme’ alleles
- The norms and averages are selected
What is directional selection
- Associated with a change in environment
- Normal phenotype is not an advantage
- Organisms who are less common and have more extreme phenotypes will be positively selected
- Positive selection in more ‘extreme’ phenotypes
What is disruptive selection?
- Opposite of stabilising disruption
- ‘Extreme’ phenotypes are selected for
- ‘Average’ phenotypes are selected against
What is genetic Drift?
Variations of allele frequency in small populations due to chance
How do genetic drift affect smaller populations?
- By chance, individuals have better breeding and so their alleles become more numerous
- Or due by random sampling during reproduction, some alleles are not passed on
What is the founder effect?
- Extreme example of genetic drift
- Small populations arise due to establishment of new colonies by isolated individuals
- Smaller populations have smaller gene pools than original population and display less variation
- If carried to new population, the frequency of alleles in the original population will have a higher population in the new, smaller population
Bottlenecks
Bottlenecks
What is a Hardy-Weinberg Principle
- A mathematical model to calculate allele frequency in a population
What are the assumptions of the Hardy-Weinberg Principle
- Population is large
- Mating within population is random
- No selective advantage for any genotype
- No mutation, migration or genetic drift
What is cystic Fibrosis
- Problems in mucus production
- Affects CTFR protein
- In Britain, 1 in 3300 babies born with cystic fibrosis
What is a species?
- A group of organisms with similar morphology and physiology, which can (theoretically or actually) interbreed with one another to produce fertile offspring.
- This is the ‘Biological Species Concept’
How to get two genetically isolated populations?
- A particular set of circumstances reduces gene flow between two populations of a species
- Over time, genetic differences between populations (caused by genetic drift) starts to accumulate
- Once sufficient changes occur, the populations may become reproductively isolated
- This reproductive isolation can be either pre-zygotes or post-zygotic
What is allopatric speciation?
Physical barrier that leads to geographic isolation
Environments of the different groups will be different and the selection pressures result in different physical adaptation
What is allopatric speciation?
Physical barrier that leads to geographic isolation
Environments of the different groups will be different and the selection pressures result in different physical adaptation
What is Sympatric Speciation?
- Occurs within populations of the same habitat
- Less frequent than allopatric and occurs more in plants
- Members of two different species interbreed and form fertile offspring
- The hybrid formed will have a different no. of chromosomes and no longer interbreed with neither of the parent population
- This stops gene flow and isolates the hybrid population.
What is artificial selection?
- An evoluntary process in which humans consciously select for or against particular features in organisms
How and why do we selectively breed animals?
- By selecting a breeding of animals for with desirable characters by farmers
- E.g. high resistance to disease, high crop yields, producing better quality of food
How and why do we selectively breed plants?
- Plants cross with plants to form hybrids more frequently than animals
- This happens by the release of the large number of pollen grains
- High growth rate, high crop yield
What are the potential problems of selective breeding?
- Limiting the gene pool and decreasing genetic diversity reduces the chances of inbred organisms adapting to the changes of the environment
- Many genetic disorders can be produced e.g. cystic fibrosis (same recessive alleles)
- Pedigree dogs are used to trap animals for people to hunt, fighting or herding
- Big dogs often have heart and hip problems.
What are gene banks?
- Store biological samples like seeds, sperms and eggs
