Population and Evolution Flashcards
define species?
a group of similar organisms that can reproduce to give fertile offspring
define population?
a group of organisms of same species living in particular area at particular time - have potential to interbreed
define gene pool?
complete range of alleles present in population
define allele frequency?
how often allele occurs in population
what does the hardy weinberg principle predict?
that frequencies of alleles in population wont change from one generation to the next
what is the hardy weinberg principle only true under?
HAS to be
- large population
- no immigration
- no emmigration
- no mutations
- no natural selection
- RANDOM mating
what can the hardy weinberg principle be used to calculate?
frequency of particular alleles, genotypes and phenotypes within populations
hardy weinberg equation used to predict allele frequency?
p + q = 1
p = frequency of one allele - dominant
q = frequency of one allele - recessive
hardy weinberg equation to predict genotype and phenotype frequency?
p^2 + 2pq + q^2 = 1
p^2 = frequency of homo dominant
2pq = frequency of hetero genotype
q^2 = frequency of homo recessive
define variation?
differences that exist between individuals
variation within a species means…
individuals in pop show wide range of diff phenoypes
what causes genetic variation within a species?
when same species have same genes but diff alleles
what is the main source of genetic variation?
mutations
how can genetic variation be introduced?
during MEIOSIS
- crossing over chromatids
- independent segregation
- random fertilisation of gametes
what variation only results in evolution?
genetic
define evolution?
frequency of allele in population which changes over time
natural selection is one methof by which…
evolution occurs
define selection pressure?
anything that affects an organisms chance of survival and reproduction
stabilising selection?
individuals with alleles for characteristics towards MIDDLE range more likely to survive and reproduce
when does stabilising selection occur?
when enviro not changing
- reduces range of phenotypes
stabilising selection e.g.
RANGE OF FUR LENGTH
- in stable climate, having fur at extremes reduces chance of surviving and reproduction
- harder to maintain right body temp
- those with average fur length more likely to survive, reproduce & pass on alleles
- proportion of population with average fur length inc
- range of fur length dec
directional selection?
individuals with alleles for single EXTREME phenotype more likely to survive and reproduce
when directional selection occur?
in response to enviro change
example of directional selection?
cheetahs - speed
disruptive selection?
individuals with alleles for extreme phenotypes at either end of range are more likely to survive and reproduce.
when does disruptive selection occur?
when enviro favours more than one phenotype
(CAUSES EVOLUTION)
example of disruptive selection?
beak sizes
define speciation?
development of new species from existing species
when does speciation occur?
when pop of same species = reproductively isolated
- change in allele freq changes phenotype
- no longer interbreed = fertile offspring
define geographical isolation?
what does it lead to?
when a physical barrier divides a population of species, causing some individuals to = separated from main pop
ALLOPATRIC SPECIATION
define sympatric speciation?
when population becomes reproductively isolated without any physical separation
allopatric speciation
- geographical Isolation
- environmental conditions vary between two habitats
- different selection pressures
- different alleles advantageous
- survive, reproduce to = fertile offpsring - pass on advantageous allele
- differences accumulating in gene pools - causes change in phentoype frequencies
- = reproductively isolated
sympatric speciation
- new selection pressure occurs
- populations remain in the same place
- become reproductively isolated
- both evolve because of selection pressure
- can no longer interbreed successfully
what is polyploidy?
when mutations occur that inc the number of chromosomes
why does reproductive isolation occur?
- changes in alleles and phenotytpes
- in some individuals prevent them from breeding successfully
- with individuals without these changes
what are the 3 main ways reproductive isolation occurs?
- seasonal
- mechanical
- behavioural
seasonal
individuals with same population develop diff flowering / mating seasons
/
become sexually active at diff times of year
mechanical
changes in genitalia prevent successful mating
behavioural
group of individuals that develop courtship rituals that arent attractive to main pop
what is evolution by natural selection?
when diff selection pressures can change allele frequencies in 2 geographically isolated species
define genetic drift?
when chance, rather than enviro factors dictate which individuals survive, breed and pass on alleles
genetic drift
- variation in genotypes of pop
- by chance, allel for 1 genotype passed on to offspring more often than once
- number of individuals with allele in
- changes in allele frequency in 2 isolated pop leads to reproductive isolation and speciation
what does evolution by genetic drift have a greater impact on?
pop with
- smaller pop
- chance has greater influence
in larger pop
- chance variations in allele frequency even out across whole pop
suggest an explanation for the results in the figure?
- mutation produces KDR minus allele
- DDT use provides selection pressure
- KDR minus allele in pop inc
- those with KDR minus survive, reproduce and pass on allele
- frequency of KDR minus inc in pop
- neurones remain depolarised
- no AP
- sodium ion channel protein changes shape
- DDTs shape no longer complementary
