evolution and speciation Flashcards
(16 cards)
what’re heritable characteristics determined by
the alleles of genes that’re present in an individual
whatre the sources of variation
-mutations
-meiosis
-random fertilisation during sexual reproduction
leading to small changes in DNA base sequences between individuals in a population
selection pressures
environmental factors that influence chances of survival
survival of the fittest
some individuals will have characteristics that make them better adapted to survive these selection pressures
characteristic increasing in frequency
number of individuals with a particular favourable characteristic will increase over time
population adapted to a characteristic via natural selection
eventually this favourable chaacteristic will become the most common of its kind in the population
unfavourable characteristics will decrease in frequency by same process, individuals with unfavourable characteristic less likely to survive and reproduce passing on the allele for a characteristic to offspring
eventually unfavourable characteristic is lost from the population
speciation: what is necessary for speciation to occur?
isolation between 2 populations of same species
meaning
there can no longer be gene flow between these populations
what kind of speciation is random mutations preventing 2 populations from interbreeding with each other an example of
sympatric speciation
speciation process
-2 populations may experience different environmental conditions that create different selection pressures
-different alleles will be advantages for the 2 populations
-different alleles more likely to be passed on and become more frequent in each population via natural selection
-allele frequencies in the 2 populations change over time
-over time the populations may begin to differ behaviourally, morphologically and physiologically to an extent they can no longer interbreed to produce fertile offspring
-speciation has occured
how does genetic drift change allele frequencies
-few sexually mature adults in population causing some alleles in a population to be lost
decrease in genetic diveristy
can cause populations to diverge from each other
why might allele frequencies in 2 populations change in different ways
-accumulation of random changes resulting from genetic drift
-different selection pressures
for speciation to be caused by selection pressures they must be…
different between the isolated populations
sympatric speciation
-no geographical barrier
-ISOLATION STILL OCCURS
-isolation occurs by random changes in alleles and therefore phenotypes of some individuals in a population prevent them from successfully breeding with others in the population
examples of phenotype changes that can lead to isolation:
-seasonal changes
some individuals may develop different flowering or mating seasons to other individuals in their population meaning their reproductive timings no longer align
-behavioural
e.g. changes courtship making them unable to attract a mate to breed successfully with
-mechanical changes, some individuals may develop changes in their genitalia which make them unable to mate successfully with other individuals in their population
evidence for evolution:
