18 Variation and Selection Flashcards
Genotypic variation and phenotypic variation
Differences between individuals of the same species due to differences in their genotypes.
Differences between individuals of the same species caused by both genetic factors and environmental factors.
Two types of phenotypic variation
Discontinuous variation: Differences between individuals of the same species in which there is a limited number of phenotypes with no intermediates.
Continuous variation: Differences between individuals of the same species in which there is a range of phenotypes between two extremes.
Mutation
Genetic change
They happen when there is a change in the DNA sequence of a cell. A mutation can be inherited if it happens in a gamete (sperm cell or egg cell). Mutations are how new alleles are formed.
Mutations occur naturally through DNA replication errors but some factors increase the rate of mutation. These include:
Ionising radiation such as gamma rays, X-rays and high-energy ultraviolet electromagnetic waves.
Or some chemicals.
Gene mutation
A change in the base sequence of DNA.
Adaptive feature
An inherited feature that increases the fitness of an organism, and helps it to survive and reproduce in its environment.
Adaptive features of hydrophytes
hydrophytes are plants that only grow in or on water
Large, thin leaves with most stomata on the upper surface rather than lower surface
Little or no waxy cuticle on their leaves because water loss is not a problem
Longleaf stalks with large air spaces to help them float
A reduced root system because they do not need to be anchored in the ground
Aerial flowers to attract flying pollinators
Poorly developed xylem tissue that allows the transport of water but provides little support.
Adaptive features of xerophytes
xerophytes are plants that need very little water.
A thick waxy cuticle covering the upper epidermis of the leaves to reduce water loss
Few stomata, or stomata that are sunken into pits Surrounded by hair to reduce water loss by transpiration
Curled, rolled or folded leaves, reduce the surface area available for transpiration
A thick succulent stem
Widely spread roots that are close to the surface, so the plant can absorb as much water as possible even when there is limited rainfall, or
very deep roots to reach underground water sources.
The steps of natural selection are as follows:
- There is variation in the inherited characteristics shown by individuals in a population.
- Overpopulation of offspring
- Variation in polulation, genetic variation
- Struggle for survival, a selective pressure leads to competition
- Survival of the fittest, Individuals that are better adapted to their environment are more likely to survive and reproduce.
- Increase in alles in poluation, the better adapted alels get passed on to the next generation
Antibiotic-resistant bacteria
When a person is infected with bacteria, the bacteria reproduce very quickly in the body.
As the bacteria reproduce, mutations may occur that allow them to be resistant to antibiotics.
If the infection is treated with an antibiotic, these resistant bacteria will have an advantage over the non-resistant bacteria.
They will survive the antibiotic treatment and reproduce.
They will pass the allele for antibiotic resistance to the next generation.
Soon, the population will only contain bacteria that are resistant to the antibiotic
Selective breeding
The process by which animals or plants are bred to produce offspring with particular, desirable, characteristics.
Differences between natural and artificial selection
Natural:
better adapted to survive
Takes a longer time
Artificial:
This only occurs when humans intervene
Result is populations with desired traits not necessary for survival
take shorter time
