7.3.1 Environmental selection pressures and natural selection
infectious disease
predation
competition
sexual selection
biological agents
process in which organisms better adapted for an environment are more likely to pass on their genes to the next generation
natural selection
random changes, unpredictable in direction, in allele frequencies from one generation to the next owing to the action of chance events
genetic drift
chance effects on allele frequencies in a population as a result of a major reduction in population size
bottleneck effect
chance effects on allele frequencies in a population that is formed from a small unrepresentative sample of a larger population
founder effect
external agents which influence the ability of an individual to survive in their environment
Environmental selection pressures
A phenotype that makes the greater contribution to the gene pool in the next generation has a h______ f_____ value and is said to be at a s______ a______
Phenotypes that make l_____ contributions to the gene pool of the next generation are l_____ f___ or are said to be s_______ a_____
The change in allele frequency from one generation to the next in genetic drift is r______ and this is in marked contrast to the d______ c____ that occurs in natural selection
-natural disaster
-new disease the population has not previously been exposed to
-human activity
causes for reduction in population size
a small group of organisms that starts a new population
founder population
climate change
food shortage
availability of shelter
physical agents
when any selective pressure acts on a population in the wild and produces differences in the survival and reproduction rates of variants in that population.
why natural selection occurs
can cause allele frequencies in a population to randomly change over time rather than being influenced by selection
sampling error
only a few individuals survive
bottleneck effect
the movement of alleles between interbreeding populations. When individual organisms move or migrate between populations, they are transferring their alleles from one gene pool to another if they interbreed.
gene flow
changes in environmental selection pressure leading to natural selection, genetic drift, gene flow
agents that can cause allele frequencies to change over time include
There is variation within the population’s gene pool. This is created by new alleles arising from mutations which are inheritable (some variation also comes from sexual reproduction).
There is a struggle for all individuals in the gene pool to survive. Environmental selection pressures act upon the population.
Individuals that are better adapted to their environment are more likely to survive and reproduce, passing their alleles on to the next generation.
The alleles that allow for survival will be inherited by subsequent generations and they can increase in frequency in the gene pool over time.
mechanism of natural selection
Unlike the action of ____ _____, genetic drift does not favour one allele over another
natural selection
the new population may not be ____ of the _____ population
representative, initial
the movement of individuals and their alleles into a population, and thus into a gene pool
the movement of individuals and their alleles out of a population, and thus out of a gene pool
immigration and emigration
pollutants in soil
pollutants in water
drugs (such as antibiotics)
chemical agents
the allele frequencies within the gene pool can change over time due to..
differing selective advantages within a population
In a v____ s____ population, genetic drift can lead to the d_____, and eventual l___, of favourable alleles from the gene pool.
For this reason, when a species is r_____ to one or a few s___ populations, the species is at great risk of e______
very small, decrease, loss, reduced, small, extinction
limited genetic diversity cause
due to various genetic bottlenecks
increases genetic diversity of a population when a new allele is introduced
immigration and emigration