Selection and Evolution Flashcards
What causes variation?
1) Independent assortment of homologous chromosomes during metaphase 1
2) crossing over of non-sister chromatids during prophase 1
3) random fusion of gametes during fertilization
4) gene mutation
What are the two types of phenotypic variation?
- Continuous variarion
- Discontinuous variation
What is continuous variation?
- no distinct categories
- vary between two extremes (value can fall within the range)
- quantitative
- can be plotted as normal distribution curve
Genetic basis:
- polygenes
- many alleles
- different alleles have small effects on the phenotype
- additive effect
- LARGE environmental effect
e.g: height
What is discontinuous variation?
- discrete categories
- no intermediates
- plotted as bar chart
Genetic basis:
- few genes
- few alleles
- diff alleles have large effect on characteristics
- diff genes have different effects on characteristic
- SMALL environmental effect
e.g: blood group, eye colour, haemophilia, sickle cell anemia
What is fitness?
- The ability of an organism to survive and reproduce
What are the three types of selection?
- Stabilising selection
- Directional selection
- Disruptive selection
What is genetic drift?
- Gradual change in allele frequencies in a small population where some alleles are lost or favored just by chance NOT by natural selection
What is the founder effect?
- the reduction of gene pool in a population, resulting from only 2-3 individuals starting off a new population
What is the bottleneck effect?
- a period in which the number of species falls very low, resulting in the loss of a large number of alleles, and a reduction in gene pool
What are the consequences of a reduction in gene pool?
1) less genetic diversity
2) increase in inbreeding
3) less chance of survival
4) less chance to adapt to selection pressures
What is evolution?
- A process leading to the formation of new species from pre-existing species overtime
What is a species
- A group of organisms with similar morphological behavioral and physiological features
- which can interbreed and produce fertile offspring and are not reproductively isolated
- also share same niche
What are the causes of speciation?
- Reproductive isolation
- Geographical isolation
What is reproductive isolation?
- The inability of two populations to breed with one another as species may be geographically separated or cannot produce fertile offspring
What is geographical isolation?
- The separation of two populations by a geographical barrier such as mountain range or water stretch
(populations of the same species)
What are the two types of speciation?
- Allopatric speciation
- sympatric speciation
What is allopatric speciation?
- due to geographical isolation
- barrier arises between two populations of same species
- increased rate of interbreeding
- each population has their own selection pressures
- genetic drift occurs
- advantageous alleles
- species become reproductively isolated/no interbreeding
What is sympatric speciation?
- not due to geographical isolation
- due to ecological and behavioral separation
- genetic isolation occurs
- each population has own selection pressures
- genetic drift
- reproductive isolation, two new species form
What is artificial selection?
- The selection by humans of organisms
- with desired traits to survive and reproduce
What is the process of artificial selection?
- Humans select individuals with desirable characteristics
- Breeding of the two individuals
- Offsprings are grown to adulthood, then tested
- Process continues over many generations
- until ALL individuals show desired traits
What are the pros and cons for breeding crops?
Pros:
- resistance to disease
- high-yield
Cons:
- inbreeding depression
- harmful recessive alleles being expressed
- decrease in hybrid vigour
- increase in homozygosity
- less ability to survive and grow well
What is outbreeding?
- breeding between individuals not closely related
- increases heterozygosity and hybrid vigour
- more chance of organism to grow and survive
- increases gene pool, more genetic variation
What are the pros and cons for breeding cows?
Pros:
- High milk yield
- meat production
- disease resistance
- high fertility
- docility
Cons:
- inflamed udders, so chance of infection
- heavy udders strain legs for cows - lameness
- reproductive issues
- decreased heterozygosity and hybrid vigour
What are the assumptions of the Hardy-Weinberg principle?
- no mutations
- random mating
- large population
- isolated population with no migration
- no selection pressures
- sexual reproduction
What is the equation for the Hardy Weinberg principle?
p + q = 1
where p = dominant allele frequency
q = recessive allele frequency
What factors apart from natural selection cause change in gene pool?
- genetic drift / founder effect/ bottleneck effect
- migration
- mutation
- artificial selection / selective breeding
