population and evolution Flashcards
define a population
a group of organisms of the same species that occupies a particular space at a particular time
can a species exist as more than one population
yes
define a gene pool
all the alleles of all the genes of all the individuals within a population
define allele frequency
the number of times an allele appears within a gene pool
what are conditions for the Hardy-Weinberg principle
-no mutations
- the population is isolated
- there is no selection ( all alleles are equally likely to be passed to the next generation
- the population is large
- mating within the population is random
which is the dominant allele in the Hardy-Weinberg equation
p
which is the recessive allele in the Hardy-Weinberg principle
q
what are equations that can be used in Hardy-Weinberg
p+q=1
p^2 +2pq+q^2=1
which genetic factors can variation arise from
mutations - changes in genes and r chromosomes may or may not be passed to the next generation
meiosis - a new combination of alleles are produced before they enter the gametes
random fertilisation -
what are selection pressures
the environmental factors that limit the population of a species
what does evolution by natural selection depend upon
- organisms produce more offspring than can be supported by the available food supply
- there is genetic variety within the population of all the species
- a variety of phenotypes that selection operates against
when will intraspecific competition occur
where there are too many offspring for the available resources, so there is competition between individuals
how does intraspecific competition lead to variation
the greater the numbers, the greater the competition and the more individuals that will die. but those that are suited to the environment will survive, those with resistance to disease, catch prey or find a mate better will be able to pass their allele frequencies to the next generation
tis more favourable for them
this selection process does depend upon individuals of a population being genetically different from obe another
which types of populations are more vulnerable to genetic disease
populations with little genetic variation between individuals
why is a large pop good
because there is a higher chance that the most favourable allele combination will be present within the pop
define stabilising selection
preserves the average phenotype of a population
define directional selection
changes the phenotypes of the pop by deviating either side of the mean
what is disruptive selection
favours individuals with extreme phenotypes rather from thsoe surrounding the mean
what is polymorphism
forms that are genetically distinct but exist within the same interbreeding population
define a species
a group of individuals witht the same genes but different alleles that can reproduce to produce fertile offspring
where does genetic drift occur
small population
what is genetic drift
in smaller populations there is a smaller variety of alleles within the population - therefore genetic diversity is small.so when offspring with new allele frequencies have the ability to affect the whole population
what is difference between allopatric speciation and sympatric speciation
allopatric speciation involves a geographical isolator but sympatric does not
describe sympatric speciation
there must be two populations within a group where no gene flow can occur, populations become separated because they live in different environments within the same area. or could there could be behavioural separation, differences in feeding, communication or courtship behaviour.
describe the stages of succesion
- a pioneer species will colonise the environment
- the pioneer species will change the environment
- the environment becomes less hostile for new species
- there will be an increase in biodiversity
- this is until a climax community id reachedgf
