Unit 18 - Variation and selection Flashcards
Variation
The differences between individuals of the same species
Genotypic variation
A difference between the genotypes (alleles) of individuals of the same species
Phenotypic variation
A difference between the phenotypes (physical features) of individuals of the same species
Factors of phenotypic variation
- Genetic
- Environmental
Two types of phenotypic variation
- Discontinuous variation
- Continuous variation
Discontinuous variation
When there is a limited number of phenotypes with no intermediates e.g. blood groups
Continuous variation
When there is a range of phenotypes between two extremes e.g. height
Mutations
genetic changes that happen when there is a change in the DNA sequence of a cell
Factors that can increase the rate of mutation
- Ionizing radiation e.g gamma rays, x-rays and high energy ultraviolet waves
- Some chemicals
Gene mutation
When there is a change in the sequences of bases in DNA
Inherited mutation
Occurs in a gamete
Adaptive feature
An inherited feature that helps an organism to survive and reproduce in its environment
Hydrophytes
Plants that only grow in or on water
Xerophytes
Plants that need very little water
Adaptations of hydrophytes
- Large thin leaves with most stomata on the upper surface
- Little or no waxy cuticle on the leaves
- Long leaf stalks with large air spaces to help float
- Reduced root system due to a lack of needing to be anchored
- Aerial flowers to attract flying pollinators
- Poorly developed xylem
Adaptations of xerophytes
- Thick waxy cuticle covering upper epidermis to reduce water loss
- Few stomata or stomata are sunken into pits surrounded by hair
- Curled, rolled or folded leaves to reduce surface area for transpiration
- Thick succulent stem
- Widely spread roots close to the surface
- Very deep roots
Steps of natural selection
- Variation in the inherited characteristics shown by individuals in the population
- Population produces offspring in excess to the habitat
- There is competition for limited resources
- Struggle for survival where some are more likely to survive
- Better adapted individuals survive and reproduce
- Offspring of better adapted individuals inherit alleles to make them better adapted
Example of natural selection
- Antibiotic resistant bacteria
- Pathogenic bacteria reproduces and one has a DNA mutation
- Antibiotics are used but only the drug-resistant bacterium survives
- Drug resistant bacterium thrives and reproduces
Selective breeding
When humans produce varieties of animals and plants with desirable characteristics
How selective breeding works
Only the individuals with the desired characteristics are allowed to breed
Differences between natural and artificial selection
- Natural is done naturally whereas artificial is done by humans
- Natural is more resistant to diseases and better suited for the environment whereas artificial reduces variation and becomes susceptible to environmental change
