Variation and evolution

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  • Created by: katherine
  • Created on: 10-06-13 17:00
Define continuos variation
charecters controlled by a number of genes and the differences in charecter are not clear cut
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how is varity in asexually reproducing organisms arise
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give an exsample of continuos variation
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Define discontinuos variaition
charecters that are clear cut and easy to tel apart, controlled by a single gene
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give an example of discontinous variation
The ABO goruping system
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what are tohe 2 ways in which variation arisis
Non-heritable variation or envrionmental influences, heritable variation
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Explain non heritable variation
enrionmental factprs such as diet and exerzie affecting phenotypic variation. An organism may inherit genes, eg. height, but enrionmental factors determine if tihs height is reached
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Explain heritable variation
inherited variatoin, caused by variotin in sexual reporoduction
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Name 3 ways in wihch sexual reproduction gives variety
Mixing of 2 parental genotypes in cross fertlisatoin, random distribution of chromasomes during metaphase 1, crossing over of omologus chromasoms during prophase 1
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How are numbers in poluations kept down
envronmental factors
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What limited reocurses do organisms compete for
food, shelet, light, space, mineral ions
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Which type of competition is between indidviduals of the same species
intRA specific
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Which competition is between individuals of different species
intER specific
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define the term gene pool
the total number of allels in a population at any one time
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define ther term popuation
a group of interbreeding individuals of the same species occypying the same habitat at the same time
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define the term evolution
the proces by which new species are formed form the pre existing ones ove rlong periods of time
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Defin natural selection
a process that encourages the transmission of favourable alleles and hinders the transmission of unfavourable ones so contibuting to evolution
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describe selection in the context of evolution
the process by which organisms better adapted to their envrionment survive and breed
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what is pplateion genetics concerned with
determining the relative proportions of te various genotypes present in a population.
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What is the allele frequency
the relative proportions of alllels in a population
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what names are given tot he factors that act upon the genetic equilibrium and bring about changes in in the frequency of some alleles in the gene pool
genetic drift, mutatoin, natural selection
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wher emight genetic drift be important as an evolutionary mechanism
in smal lor isolated populations
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what is the founder effect
the 'founding' individuals in a new population may have a very differne tgene frquence by chance, thereford it may undergo genetic drift and become even more different form the parental population
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define the term isolation
occurs when a barrier prevents 2 populations from breeding with one another
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the evolution of new species form existing species
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a group of similar organisms that can interbreed to produce fertile offspring
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the offspring resuling from cross breeding of different species
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whjat are the breeding sub units within a species called
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what is the name of a barrier which prevents gene exchange between demes
isolating mechanism
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what is the process of speciation
isolated demes evolve seperatly so they eventually become diffeent species with thier own gene pool
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Give exmaples of geographical isolation
a mountian or river
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What kind of speciation is htis
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what is reproductive isolation
when there are no physical barriers
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What kind of speciaoitn is this
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What are the 5 different ways htis can happen
Behavioral isolation, mechanical isolation, gametic isolation, hybrid unviaility, hybrid sterility
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explain behavioural isolation
animals with elaborate courtship may fair to attract a female of the othere deme
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explain mechanical isonlation
incompatible genetalia
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Exlain gametic isolation
in flowring plants- failure of the pollen to germinate on the stigma, in animals- sperm may fail to survivie in oviduct
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explain hybrid unavalibility
despite fertilisation , development of embryo may not occu
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what is this due to
chromasomes not matching , eg polyploidy
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explain hybrid sterility
when rganisms from diffent species breed, sets of chromasomes are different, ergo, unable to pair at meiosos so offspring unable to produce gametes, thereofre sterile
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Card 2


how is varity in asexually reproducing organisms arise



Card 3


give an exsample of continuos variation


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Card 4


Define discontinuos variaition


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Card 5


give an example of discontinous variation


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