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)
