evolution may lead to speciation Flashcards

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1
Q

why might individuals within a popualtion of a species show a wide range of variation in phenotype

A

genetic factors
- mutation : change in base sequence of DNA so new allele
- meiosis: crossing over and independent segregation
- random fertilisation: of gametes during sexual reproduction

environmental factors
- eg climate food lifestyle

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2
Q

what is evolution

A

change in allele frequencies in a population over time

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3
Q

how does evolution occur

A

natural selection
1. variation within a popualtion due to mutations
2. selection pressure eg. predation, disease, competition -> strugle to survive
3. some organisms have phenotypes providing selective advantages due to favourable alleles
4. they are more likely to survive and reproduce passing on favourable alleles
5. allele frequencies in gene pool change over many generations

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4
Q

what is directional selection

A

selection pressures/environment favours individuals with favourable combination of alleles in one direction from the mean

mean shifts in direction of favourable allele

eg. pepper moths -> polution means white to black moths

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5
Q

draw a directional selection graph

A

bell shifted right or left

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6
Q

what is stabilising selection

A

selection pressures act against two extremes of characteristics

mean stays the same

standard deviation smaller over time

eg. clutch size in birds -> too many egges means lack of food, too little eggs means may all die

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7
Q

draw a stabilising selection graph

A

bell gets skinner and taller

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8
Q

what is disruptive selection

A

selection against the mean

population becomes phenotypically divided - favours both extremes

most important for evolutionary change as could result in two sperate species

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9
Q

draw a disruptive selection garph

A

two bell shaped curved joined in the middle

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10
Q

what is speciation

A

formation of a new species from existing species

reproductive sepeation of two populations can result in the accumulation of differences in gene pools

new species when inability of member of the population to interbreed and produce fertile offspring

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11
Q

what are the two types of speciation

A

allopatric and sympatric

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12
Q

what is allopatric speciation

A

geographical isolation
seperate gene pools, no interbreeding
mutations cause genetic variation in each population
different selection pressures act on each population
leading to natural selection of different favourable alleles
different survival and reproductive success
leads to change of allele frequencies over a long time
memebers of different populations cant interbreed to produce fertile offspring so new species arise

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13
Q

what is sympatric speciation

A

popualtion in the same area
genetic variation due to mutations
resulting in a mechanism that makes individuals reproductively issolated
- gamete incompatibility
- temporal - different breeding seasons
- behavioural - different courtship behaviour
- mechanical - incompatible genitalia
different slectional pressures
leads to xhnage in allele freq within gene pools/ divergence of gene pools
members of diffrent popualtions cant interbreed to produce fertile offspring = new species = speciation

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14
Q

what is genetic drift

A

mechanism of evolution in which allele freq of a population change over time

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15
Q

when is gentic drift strongest

A

in small poulations as chance has greater influence

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16
Q

what are the effects of genetic drift

A

doesnt take into account how favourable or harmful an allele is
bottleneck effect - when a poulation is sharply reduced in size
founder effect - when a samll new colony forms from a main population