Unit 7 Flashcards
when using Mark Capture Release, why may there be inaccurancies:
sample too small
too short a time to mix evenly
birth/death
immigration/ emigration
marking method affected behaviour
mark-release-capture assumptions:
no immigration/ emigration
few births/ deaths (no losses to predation)
proportion of marked and unmarked in both samples is the same as proportion in the habitat
marked individuals evenly distribute themselves within the population
marking aren’t lost
markings do not affect survival
why do small populations have lots of genetic disease:
small founder population/ common ancestor
genetic isolation, small gene pool
inbreeding
reproduction occurs before symptoms apparent so no selective advantage
Hardy Weinberg Principle
there is an equilibrium between allele frequencies, and there is no change in this between generations
the assumption for the Hardy-Weinberg equations:
No mutations or selection
Isolated and large population
Random mating
Genetic bottleneck:
a sharp reduction in the size of a population
produce smaller population with reduced genetic diversity
in subsequent generations, diversity remains lower
slowly increases due to random mutation
Examples:
Environmental event (floods, fires)
Human activities (Hunting, habitat destruction)
founder effect:
small group of individuals break off to form a smaller colony
founding individuals may not represent the full genetic diversity
evolve in different direction if they are subjected to different selection pressure and if the population is missing alleles
sympatric speciation:
occurs in the same habitat
mutation causes variation (link to specific phenotype)
reproductive isolation
different alleles passed on - changing allel frequency
disruptive selection occurs
eventually different species formed - cannot interbreed to produce fertile offspring
Allopatric Speciation
geographical isolation
seperate genes pools/ no interbreeding or no gene flow
Variation due to mutation
different selection pressures/ habitats
differential reproductive success
leads to a change in allele frequency
why may there may be a time lag between the prevalence of an allele and the introduction of a selection pressure:
initially, only some individuals have a favouravle mutation
differential reproductive success
individuals with favourable allele will have offspring
take many generations for mutation to become the most common allele
processes by which stabilising selection occurs:
unchanging conditions of environment
variation between individuals due to mutation
extreme phenotypes selected against/ less likely to survive and reproduce
small variation in allele frequency
mean value is unaltered/ range is reduced
increasing proportion of populations become well adapted to the environment
effects of disruptive selection:
selection against the mean
population become phenotypically divided - favour both extremes
could result in 2 species
main effects of stabilising selection:
selective pressures favour the mean/ acts against the 2 extremes of a characteristic
individuals with extreme phenotypes less likely to survive ( standard deviation gets smaller over time)
Mean stays the same
process of natural selection:
Variation within a population due to mutation
selection pressures => struggle for survival
some organisms have alleles that are more favourable to the selection pressure
these organisms are more likely to survive and reproduce, producing more offspring and passing on their favourable alleles
allele frequencies in gene pool change over many generations
how is grassland management an example of conservation:
Vegetation growth rate slows significantly due to heather burning and sheep grazing
Burning maintains plant vigour and removes unwanted vegetation
Prevents climax community from being reached as the young tree saplings are destroyed => stopping progression into deciduous woodland
