Population, evolution, speciation, artificial selection Flashcards
Continuous Variation
A characteristic that can take any value within a range e.g height
Discontinuous Variation
A characteristic that can only result in a discrete value e.g blood type
Cause of continuous variation
Both genetic (polygenic) and environmental factors
Causes of discontinuous variation
Mostly genetic
What are three types of selection pressures that can affect evolution
Stabilising, directional and disruptive
What is stabilising selection?
A type of natural selection where intermediate phenotypes are favoured and extremes are selecting against, creating consistency e.g medium sized peacocks
Directional selection?
A type of natural selection that occurs when an environmental change favours a new phenotype= changes population mean e.g black peppered moth
Genetic drift
Change in frequency of an existing allele in the population due to random chance/event
Genetic bottleneck
When a population size shrinks and increases again- caused by the events that kill almost the the whole population only leaving a few individuals— reduces gene pool
What does the Hardy Weignberg equation assume?
- Large population sample
- Mating is random
- No mutation, genetic drift or founder effect
Population
Members of a species living in the same place at the same time that can interbreed
What are isolating mechanisms/speciation in organisms?
Mechanisms that divide populations into subgroups and could lead to evolution of new species
Allopatric speciation
Formation of two different species from one due to geographical isolation
Sympatric speciation
Formation of two different species from one due to reproductive isolation, while two populations inhabit the same geographical location
Artificial breeding
Selective breeding of organisms where humans choose desired phenotypes and interbreeding them individually
What can artificial breeding lead to?
Interbreeding depression- Inheritance of harmful recessive alleles due to homozygosity
Hybrid vigour
Crossing individuals from seperate gene pools to obtain heterozygous alleles
What are desirable characteristics in crops that a selectively bred for?
- Drought tolerance
- Increased yield
- Resistance to insects
- Shorter ripening time
Desirable characteristics for livestock
- Higher milk yield
- Leaner meat
- Increased wool production
Ethical considerations of selective breeding of dogs
- Susceptible to diseases due to inbreeding
- Body pains
Ethical considerations of selective breeding of livestock
- More lean meat (die at colder temsps)
Why can a genetic bottleneck lead to low genetic diversity?
Many alleles are lost when population drops and modern population descends from few survivors
Founder effect
The reduction in genetic variation that occurs when a small group of individuals becomes relocate to an isolated area from a larger population— small pop breeds = small gene pool
