artificial selection and natural selection Flashcards
What is stabilising selection?
Allele frequency does not change over time
Natural selection leading to constancy within a population
A mix of phenotypes are favoured and extreme phenotypes are selected against
- Reduces genetic variation
- Alleles for extreme phenotypes may be removed from the population
What can stabilise or destabilise a population?
Environmental forces can stabilise a population leading to genetically similar over time
Or destabilise a population leading to evolution or adapting to the environment
What is directional selection?
Type of natural selection that occurs when an environment favours a new phenotype and so results in a change in a population mean
What are the two types of isolating mechanisms?
- Geographical
- Reproductive
What is the geographical isolating mechanism?
Population is separated by geographical features
- Subjected to different selection pressures
- Undergo independent changes to allele frequencies or chromosome arrangements within their gene pools
- Leads to allopatric speciation
What is allopatric speciation?
Formation of two different species from one original species, due to geographical isolation
What is reproductive isolation?
Caused by a biological and behavioural changes, genetic changes, within a species
For example:
Mutation leads to some members changiing their foraging behaviour - members of the diurnal population will be unlikely to mate with the crespular and nocturnal population
- Leads to sympatric speciation
What is sympatric speciation?
Formation of two different species from one original species due to reproductive isolation, while populations inhabit the same geographical location
What is artificial selection?
Selective breeding of organisms involved humans choosing the desired phenotypes and interbreeding those phenotypes individually
Therefore selects the genotype that contribute to the gene pool
What are examples of artificial selection?
3x
- Cereal - resistance to pests
- Cattle - milk, meat, leather
- Poultry - eggs, meat, feathers
What is interbreeding?
Gene pool of the selected breed is reduced
Chances of an individual inheriting two copies of a recessive harmful allele are increased
What is hybrid vigour?
Outcrossing individuals belonging to two different varieties to obtain indiviuals that are heterozygous at many gene loci
More healthier
What are ethical considerations of artificial selection?
3x
- Traits in dogs that are considered desirable by humans might put dogs at a selective disadvantage if they had to survive in the wild
- Some breeds, through inbreeding from, a limited number of pedigree dogs have susceptiability to disease
- Some coat colours, selected because humans like the look of them, would also fail to camouflage
What are conditions that certain dog breeds are susceptible to?
- Boxer - cancer and heart disease
- West highland terrier - Dry eye; skin irritations and infections
- Dobeman - heart failure; spinal cord deformity and paralysis
What is founder effect?
When a small sample of an orginal population establishes in a new area
Its gene pool is not as diverse as that of the parent population
What is bottleneck?
Sharp reduction in size of population due to environment catashtrophes suhc as earthquakes, floods, diseases or human activities such as genocide or habitat destructions
What is genetic drift?
Genetic makeup of a population changes due to the effect of random sampling
Arises as a result of genetic bottlneck or founder effect
