evolution and populations in ecosystems Flashcards
what genetic factors cause variation within a species
mutation
random segregation of alleles in metaphase I meiosis
crossing over between chromatids of homologous chromosomes
random mating of organisms within a species
random fertilisation
what is mutation
mutation is a change to the DNA
mutations can either be a gene mutation or a chromosome mutation
what environmental factors could cause variation
diet
disease
predators
explain how natural selection causes a change in allele frequency
organisms produce more offspring than are needed to replace the parents. most population numbers remain the same
this causes competition for existence
individuals in a species show variation.
those with advantageous alleles will survive. (survival of the fittest)
these individuals reproduce, passing on their advantageous allele
this will shift the allele frequency within the gene pool
what are the three types of natutral selection
Stabilising selection
directional selection
disruptive selection
explain stabilising selection
stabilising selection is the elimination of extreme variations in a population
e.g bettle colour- light and dark beetles may be easy to see but all those in th middle may camouflage well
define natural selection
the process by which heritable traits become either more or less common in a population due to pressures from the environment
directional selection
if an environment changes one extreme form of a trait may be favoured
e.g peppered moth frequency in industrial revolution. darker moths became harder to see so were selected for.
disruptive selection
both extremes in a trait are selected for but the middle is disadvantageous so is selected against
opposite of stabilising
e.g salmon male size
large fish can fight off opponents to fertilise eggs, small ones are fast enough to sneak in and fertilise the eggs, medium fish are selected against
evolution
is the shift of allele frequency in a gene pool caused by selection pressure
what is speciation
the formation of new species
what are the 2 forms of speciation
Allopatric
sympatric
describe allopatric speciation
the developement of new species due to a physical seperation of a species
population seperated by geographical isolation e.g sea, mountain range etc
isolated populations subjected to different selection pressures.
natural selection causes a shift in the gene pool, resulting in the two populations being reproductively isolation and therefore a new species has evolved
describe sympatric speciation
new species formed when there are no physical barriers- reproductive isolation due to:
- behaviour- mates attracted by calls and dances etc
- structure- sex organs incompatible
- gamete mortality
- hybrid inviability- may result in a zygote that cant divide
- hybrid sterility- two species mate to form a hybrid but this cant reptroduce
- polyploidy- failure of separation of chromosomes in meiosis
genetic drift
changing of allele frequency due to chance.
e.g forest fire wipes out large proportion of population but at random- not due to an advantage that they have
this has a larger affect on a smaller population
