Natural Selection and Microevolution: Unit 4, Topic 2 Flashcards
What is natural selection?
- the process where organisms better adapted to their environment tend to survive and produce more offspring.
- transmitting favourable traits through generations, unfavourable traits die.
- phenotypes can confer a survival advantage in the changed environment, or they can give a disadvantage.
viability: the ability to survive or live successfully
fecundity: the ability to produce an abundance of offspring or new growth
positive selection: selection for a heritable trait
negative selection: selection against a heritable trait.
What are environmental selection pressures?
climatic conditions: flood, drought, extreme temperature changes
competition for resources: availability of food and water, shelter, mate availability, predator abundance
What is a gene pool?
- the sum total of all alleles found in a population
population: same species/ live in the same geographical area/ readily interbreed to produce fertile offspring.
The range of variation possible in a population is restricted by the alleles available in its gene pool
Fixed gene: genes that only have one possible allele in a gene pool and thus do not contribute to any variation.
What is allele frequency?
- the relative proportion of a particular allele in a population (how common the allele is)
- can change overtime
- microevolution is a change in the frequency of alleles in a population
- selection of alleles can be positive or negative
negative: limits the ability to survive and adapt to changes
positive: helps ensure the survival and ability to adapt to changes of a species.
what are the factors influencing allele frequency?
variation: genetic differences
viability: survival determined by environmental factors
reproduction
fecundity: rate of production and number of offspring
survival
environmental selection pressures.
What are the three main types of phenotypic selection?
stabilising, directional, and disruptive.
stabilising selection:
- The environment of an organism is stable
- selective pressures will act against deleterious alleles that cause a departure from the optimal phenotype.
- favours organisms similar to their parents
- favours average
Directional selection:
- changes in the environment lead to selective pressures favouring organisms with one of two extreme traits.
- leads to change in traits over time
- one of two extreme phenotypes is favoured
- allele frequency shifts over time in the direction of that extreme phenotype
Disruptive selection:
- operates in favour of extreme and against intermediate forms
- selects against the average individuals in the population
- favours both extremes
What is a mutation?
- the ultimate source of genetic variation as they introduce new alleles into the population.
- mutations can lead to phenotypic changes that limit long-term survival.
- may or may not lead to phenotypic change
- mutations that do not change the amino acid sequence would not affect phenotype.
What is a gene flow?
- the transfer of alleles into or out of a population
- results from emigration and immigration
- a result of migration of individuals that reproduce in their new opulations, or movements of gametes such as pollen transfer.
What is genetic drift?
- allele frequencies of a population change over generations due to chance.
- effects are strongest in small populations
- occur in small populations or when a large population is suddenly reduced.
What is bottleneck effect?
- types of genetic drift
- caused by sudden disaster
- A catastrophic decrease in population size can result in the loss of some alleles from the gene pool.
other genes can be preserved by chance
What is the founder effect?
- occurs when a few individuals carry alleles to a new, isolated area = new population is formed with different allele frequencies from the original population
less genetic diversity than the original population - recessive alleles may have a higher chance of coming together.
