population genetics Flashcards
hardy weinberg equation
can be used to predict allele frequencies in the population.
gene pool
all of the alleles of all genes within the population at one time.
population
all individuals of the same species in the same area at one time.
allele frequency
proportion of an allele within the gene pool.
speci
genetic factors- mutations
sudden changes in gene or chromosomes
main source of variation
may or may not be passed onto next generations
genetic factors- meiosis
crossing over and independent segregation
nuclear divions
new combinations of alleles before they go into gametes.
genetic factors- random fertilisation
random fusion of gametes
sexual production- new combinations of alleles- genetic variation among offspring.
enirovnmental factors
influences organism’s expression of genes.
genes set limit but environment determines where within these limits organisms can survive e.g.
food availability
pH
soil conditions.
human environmental factors
height and mass
polygenes
e.g. height would produce a normal distribution curve.
what is genetic diversity?
total number of different allles of a gene in a population
what is required for natural selection to occur?
natural selection can only occur when there is genetic diversity within the population.
what does natural selection lead to?
evolution- change in allele frequency over many generations within a population.
what are the 3 types of adaptations?
anatomical
physiological
behavioural
evolution via natural selection
mutations produce a new allele
in certian environmental conditions, organisms with this allele have a selective advantage and are more likely to survive and reproduce
this allele is inherited by their offspring.
over many generations, the frequency of this allele increases in the population.
directional selection
organisms with extreme phenotype have selective advantage
modal/most common trait changes
occurs when there is an environmental change.
e.g. antiobiotic resistance in bacteria.
stabilising selection
modal/most common trait remains the same
occurs when there is no environmental change
standard deviation/range decreases as number with extreme phenotype decreases
e.g. birth weight of babies.
what is differential reproductive success?
all organisms are not as likely to reproduce which leads to changes in allele frequency within the gene pool.
disruptive selection
individuals with alleles for either extreme phenotype have a selective advantage/are more likely to surive and reproduction
frequency of middling trait decreases
more individuals with extreme alleles
continuous disruptive selection ultimately leads to speciation.
2 ways that populations can become reproductively isolated
geographic barrier- allopatric
changes in reproductive mechanisms- sympatric.
allopatric speciation
reproductive isolation due to geographical barrier e.g. mountain ranges or bodies of water separating land masses
2 populations accumulate different beneficial mutations to survive in their environment.
their DNA differences become so siginificant that they can no longer interbred to produce fertile offspring- so there are now 2 different species.
allopatric speciation
reproductive isolation due to geographic barrier e.g. mountain ranges or bodies of water separating land masses.
2 populations accumulate different beneficial mutations to enable them to survive in their environment.
DNA differenes are so significant over time that organisms cannot interbred to produce fertile offspring- 2 different species.
sympatric speciation
-may not be a geographic barrier, but organisms are unable to interbreed
-random mutation could cause changes in courtship behaviour e.g. fertile at different times of year/different courtship rituals.
over time, reproductively isolated populations accumulate different mutations- can no longer interbreed to produce fertile offspring.
genetic drift
genetic drift is the changes in allele frequency between generations within a population
genetic drift will always occur between generations but continual, substantial genetic drift will lead to evolution
evolution occurs more rapidly in smaller populations as they are more affected by changes in allele frequency.