4.4 variation and Evolution Flashcards
Evolution: definition
a change in the average phenotype of a population
Speciation: Definition
formation of a new species
species: definition
group of organisms that can interbreed to form fertile offspring
when will evolution not occur
if the conditions under which the Hardy Weinberg principles apply
Can be speciation be due to
-genetic drift (in isolated populations)
-founder effect in small populations
-natural selection
what is the founder effect
when a small population has become separated from the original population and so an allele in the small population becomes more frequent in future generations
what is allopatric speciation
where a new species evolves as a result of geographical isolation/ physical barriers (mountains, deserts)
prevented from interbreeding
what is the isolating mechanisms in allopatric speciation
geographical isolation
what is sympatric speciation
when organisms living in the same niche become reproductively isolated into 2 groups for non-geographical reasons
what are non-geographical reasons
pre-sygotic
post-zygotic
example of a pre-zygotic reason
can be behavioural, morphological, gametic or seasonal
example of post-zygotic reason
hybrid in viability/sterility and breakdown
6 steps of natural selection
- mutation
- variation
- competition advantage
- survival of the fittest
- reproduction
- Pass on advantageous alleles
what does mutation in alleles lead to
speciation by natural selection
lead to changes in allele frequency
speciation by natural selection
how phenotypes can be changed or maintained to be optimal in the environment
reason for variation in phenotypes
speciation by natural selection
due to different alleles
after many offsprings are produced what happens?
speciation by natural selection
there is a competition for limited resources
what is selection pressure
speciation by natural selection
some phenotypes get a survival advantage (long enough to breed)
what happens to successful phenotypes
speciation by natural selection
they pass on their alleles increasing their frequency in the population
purpose of a T test
whether the difference between the mean of 2 groups is down to chance or another factor
Deme: definition
group of individuals within a population who breed with one another, it is possible for individuals from different deems to interbreed
genetic drift: definition
the change in allele frequency in a population by chance, (more noticeable in small populations )
what is the variation in genetic drift
it is by chance
gene pool: definition
all the alleles present in a population at a given given time
when will a gene pool remain constant
if:
-population is large
-no selection pressure
-mating is random
-no mutations occur
-all genotypes are equally fertile
-no emmigration/immigration
explain the Hardy-Weinberg Principle
-the frequency of alleles and genotypes within a population will remain constant from one generation to the next
what is needed for Hardy Weinberg equillibrium
certain conditions are needed:
-large population
-no selection for/against any phenotype
-random mating
- no mutations
-isolated population
what is the H.W equation
-estimate the frequency of dominant/recessive or of different genotypes within a population
H.W equation
p=
frequency of dominant alleles (A)
H.W equation
q=
frequency of recessive allele (a)
H.W equation
p+q=
1.0
H.W equation
p2=
frequency of AA
H.W equation
2pq=
frequency if Aa
H.W equation
q2=
frequency of aa
variation: definition
the phenotypic difference between organisms of the same species
2 types of variation
heritable/non-heritable
what is heritable variation
due to genetic reasons (by crossing over, independent assortment, sexual reproduction, epigenetics) can be passed on to offspring
what is non-heritable variation
due to environmental reasons, cannot be passed on
what is continuous variation
-characteristics have many possible values
- no distinct categories
-generally polygenic (controlled by many genes)
-gene expression influence by the environment
-forms a normal distribution curve
example of continuous variation
height, weight, finger length, leaf length
what is discontinuous variation
-no intermediate types
-only a small number of possibilities
-characteristics are distinct
-monogenic (controlled by a single gene)
-gene expression not influenced by the environment
-bar chart
example of discontinuous variation
blood group, eye colour
what factors affect population of organisms
biotic factors- predationm parasites, disease, competition
2 types of competition
intraspecific
interspecific
what is intraspecific competition- what is competed for
between members of the same species (competition for mates/space)
what is interspecific competition- what is competed for
between different species (compete for for the same resources)
role of advantageous alleles
increase the likelihood of survival, organism survives and passes on the successful allele
explain selection pressure
the effect of selective agencies on the phenotypes in a population (can alter the frequency of alleles)
i.e food availability, climate, human impact
FOR selection pressure
phenotypes have an advantage in competition so the alleles that code for them are selected FOR
AGAINST selection pressure
phenotyoes do not have an advantage and are unable to compete successfully. alleles that code for them are selected against.
different types of selection types
stabilising
directional
disruptive
definition of stabilising selection types
the average trait is selected for
does stabilising selection lead to speciation
unlikely no
examples of stabilising speciation
tail size for a cat
too small=lack balance
too long= drags on the floor
average size=aid survival
what is directional selection type
one extreme is selected for
change the characteristics of the population
does directional selection lead to speciation
unlikely no
examples of directional selection
lizard tail length, long tail is selected as it looks like a snake so will scare off predators
what is disruptive selection
either extreme is selected, average trait is selected against
does distruptive selection lead to speciation
Yes
example of disruptive selection
rabbits. small rabbits may run faster, fit down smaller holes. large rabbits are able to fight back better. both selected over average size rabbits
