Ch 9 Flashcards
when does natural selection occur
when selection pressures in the environment confer a selective advantage on a specific phenotype to enhance its survival and reproduction; this results in changes in allele frequency in the gene pool of a population
what can contribute to changes in allele frequency
environmental selection pressures, sexual selection, mutation, gene flow, selective breeding and genetic drift
what needs to be considered to conserve viable gene pools
biogeography
reproductive behaviour
population dynamics
what percentage of our gene are ‘fixed’
80-85%
gene pool is…
the total collection of alleles within a population
what 6 factors can effect allele frequency
mutation of an allele
immigration & emigration of individuals
reproduction rate of various individuals in the population
genetic drift
the bottleneck effect
the founder effect
bottle neck effect
when the size of a population is drastically reduced & certain alleles may be lost through chance
founder effect
when a few individuals move to a new area & become isolated from a larger population e.g. the amish community
deleterious recessive alleles may have a higher chance of coming together
what are the principles of natural selection
individuals show variation from one another, within a population
many variations are caused by mutations in alleles & are inheritable
more offspring are born than can survive to maturity & reproduce; there is a struggle for existence & only some organisms can reproduce
some individuals have traits that make them more suited to their environment than others, making them more likely to reproduce & pass on their alleles
what’s artificial selection
parental stock with certain desirable traits are selected and mated; over time, new traits can be established in later populations
list 5 Selection pressures
competition between species for food & territories
predator-prey relationships
competition within species for food or water
competition within species for territories/nesting places
sexual selection
what’s sexual dimorphism
when males and females have different appearances
microevolution
the outcome of natural selection pressure shows a change in the frequency of various alleles within a population; any change in the gene pool of a population.
macroevolution
major evolutionary changes above the species level
true or false; speciation and macro-evolutionary changes result from an accumulation of micro-evolutionary changes over time
true
speciation
when a species disappears only to be replaced by a new organism
what are 4 pre-reproductive isolation mechanisms
geographic
temporal (time)
behavioural
morphological (can no longer mate)
what are 3 post-reproductive isolation mechanisms
gamete mortality – the gametes don’t survive
zygote mortality – zygote forms, but doesn’t survive
hybrid sterility – an infertile offspring survives e.g. mule
what’s allopatric speciation
when gene flow is disrupted as populations become physically separated through geographical isolation (populations diverge)
What may cause sympatric speciation
may feed on different things
choose mates based on different characteristics
mate at different times
pre & post zygotic factors
Why are larger populations more resistant to change
large populations hold a greater reserve of different alleles to draw on as selection pressures change
stabilising selection
when an environment is unchanging, then selection pressures act against deleterious alleles
direction selection
Changes in the environment lead to selection pressures to favour new traits, changing the gene pool over time
disruptive selection
when both extreme traits are favored in an environment. Disruptive selection increases genetic and phenotypic diversity in a population, since more than one phenotype, or physical trait, is favored.
results in divergence
