selection and speciation Flashcards
describw what is meant by speciation (allopatric)
- geographical isolation
- separate gene pools/no interbreeding
- variation due to mutation
-different selection pressures - selection for advantageous allele
- dofferential reproductive success
- change in allelic frequencies
describe the process of succession
- colonisation by pioneer species
- pioneers cause change in environmental a/biotic factors
- pioneers make environment less hostile for new species
- new species make conditions less suitable for previous species
- change in biodiversity
-stability increases - climax community
causes of variation
- mutation
- meiosis
-random fertilisation of gametes
discontinuous variation
caused predominately by genetic factors
- produces categoric data
- single gene
eg: human blood groups
climatic conditions
temp
light intensity
humidity
continuous variation
- polygene (more than one gene)
eg: height and mass - normal distribution curve
natural selection
individuals better adapted to environment
more likely to survive and reproduce
increasing allelic frequency of advantageous allele within popultion
natural selection
variation due to mutation
differential survival: thoe with beneficial alelles more likely to survive and reproduce
selection pressure introduced
those with advantageous allele more likely to survive and reporduce
differential reproductive success
increase in allelic frequency
over many generations
stabilising selection
- occurs when stable environment
eg: baby birth mass weight - selection pressure at both ends of distribution
- favours average, eliminates extremes. increases proportion of population that is well adapted to environment
- when SD decrease, mean unaltered
- reduces variability
- reduces opportunity for evolutionary change
directional selection
- mean: optimum phenotype for existing conditions
- selection pressure introduced, favours new extreme phenotype
eg: antibiotuic resistance
disruptive selection
- selection pressure favours extreme phenotypes
- least common, most important in selection
species
group of individuals with similar characteristics and same genes
capable of interbreeding to produce a fertile offspring
- same gene pool
speciation
evolution of a new species from an existing species
must undergo:
- reproductive isolation (prevented period of interbreeding)
this will cause accumulation of mutations and different selection pressures
hardy weinberg principle
allelic frequencies in a population will remain constant from one generation to the next, provided there is:
- random fertilisatioon of gametes
- no selection
- no migration
- no mutations
- a large population
genetic drift/ bottleneck
random change in allelic frequencies
eg: natural disaster
gene flow/ founder effect
change in allelic frequency due to the migration of fetile individuals
eg: migration
allopatric speciation
physical barrier dividing a population (eg: river, mountain, road)
- geographically isolated
- different slection pressures
- mutations accumulate
- reproductively isolated (cant interbreed to form a fertile offspring)
sympatric speciation
same area
become reproductively isolated for some reason (eg: choice of food/season to mate/active after hybernation)
isolating mechanisms list
- allopatric
- sympatric
- temporal
- ecological
- behavioural
- mechanical
- gametic
- hybrid
temporal isolation
breed at different times of the year
ecological isolation
different habitats in the same area
behavioural isolation
different behaviour patterns (ie: different courtship behaviour)
mechanical isolation
anatomical differences making it impossible for gametes to come together
gametic isolation
incompatibility between gametes prevent hybrid from forming (eg: sperm may be destroyed in vagina for females, too acidic)
hybrid
organisms interbreed but offsprings are infertile
(eg: horse and donkey = mule)
hybrid
organisms interbreed but offsprings are infertile
(eg: horse and donkey = mule)
sympatric speciation process
- occurs within same habitat
- gene pools remain separate/ no gene flow
- different alleles are selected for/ change in frequency of alleles
- disruptive selection
- eventually species can not interbreed to produce a fertile offspring
individuals in a populatuion shwo phenotypic variation. give two factors that cuase variation.
genetic crossing over
environmental factors
what is allopatric speciation?
population separated into different geographical regions
- formation of new species from geographically isolated populations
what is sympatric speciation?
formation of new species from existing species without geographical isolation
