3.7.3 Evolution may lead to speciation (C18) Flashcards
What do you call the environmental factors that limit the population of a species?
selection pressures e.g. predation, disease, competition
Define gene pool
All of the alleles of all of the genes of all the individuals within a particular population at a given time
All populations have the potential to increase exponentially - why in nature is this rarely the case
death rates must be high which is compensated for by the high reproductive rates. Some species have lower reproductive rates but have higher degree of parental care , the lower death rate from this maintains their population size.`
What is the consequence of over-production?
competition between individuals - intraspecific
What determines which individuals survive in over production?
The best adapted organisms to the conditions at the time survive and reproduce and pass on favourable allele combinations.
Why do organisms NOT produce organisms identical to itself when it survives the condition it lives in?
Meiosis - offspring produce show variation from the parent, this may may result in offspring more or less likely to survive. Environment changes all the time, this way there is an wide range of genetically different organisms in the population.
Consequences of populations showing little genetic diversity
more vulnerable to disease and climate changes.
A larger population showing greater genetic diversity means
There is a greater chance that one or more individuals will have the correct combination of alleles for survival
Individuals that survive the struggle for survival can
more likely to breed/reproduce, pass on favourable allele combinations to future generations.
Name 3 types of selection
stabilising, directional and disruptive
Describe stabilising
preserves the average phenotype, selection against extreme phenotypes. Environment pretty stable
Describe directional
Phenotype of population changes, favouring phenotype at one direction from the mean (selection for one extreme phenotype). Environmental conditions change.
Describe disruptive
Preserves individuals with extreme phenotypes (both ends), not those around the mean. Opposite to stabilising. Least common selection. Environment changes taking 2 distinct forms
which types of selection is being described: A baby born with a birth weight of more than 4kg and less than 2.5kg has a greater risk of dying
stabilising
Elephants have evolved longer trunks enabling them to reach leaves higher up in the trees
directional
small mammals can escape from predators by hiding in small places while large mammals can resist attack from predators
disruptive
the most important selection in bringing about evolutionary change
disruptive
define speciation
the evolution of a new species from an existing one
define a species
group of similar organisms that are capable of breeding and producing fertile offspring - they share a common ancestry (same genes different alleles)
summarise how a new species is formed
because of reproductive separation, variation followed by natural selection
define adaptive radiation and consequences of this
when each population becomes adapted to its local environment, leading to changes in allele frequency in the population
identify 2 forms of speciation
allopatric and sympatric
the genetic diversity of a small population can be described as
Less - as there is a smaller variety of alleles in a small populations
the genetic diversity of a large population can be described as
Great - as there is a larger variety of alleles in a large populations
The effect of genetic drift is greater on which population size - small or large?
small
Allopatric means
different countries
Allopatric speciation means
When 2 populations become geographically isolated
Examples of geographical isolation…
physical barrier which prevents interbreeding e.g. oceans, rivers, mountains, deserts.
Define reproductive separation
when 2 populations can no longer interbreed and produce fertile offspring
Example of allopatric speciation
Finches on the Galapagos Islands!
Sympatric means
same country
Sympatric speciation occurs
within a population of organisms living in the same area (doesnt require geographical isolation)
sympatric speciation arises because
they have different breeding seasons, they may inhabit different habitats in the same area so never meet, anatomical differences,
Name the type of selection shown
stabilising
name the type of selection shown
directional
name the type of selection shown
disruptive
main source of variation within the same species
mutation (creating different alleles)
mutations in DNA creates
new alleles - new characteristics
Variation between species is also brought about during
meiosis
variation is also brought about between members of the same species because of the …
environment
What does evolution do to the frequency of alleles in a population?
changes them - increase or decrease
What happens to the frequency of the alleles that give organisms an advantage?
increases
What happens to those organisms that are better adapted to the selective pressures in the environment?
survive, reproduce and pass on favourable alleles
What happens to the environment in stabilising selection?
it doesnt change
What happens to the phenotype during stabilising selection?
preserves the middle of the range phenotypes
Which phenotype is selected for during directional selection?
an extreme phenotype - these are more likely to survive and reproduce
What phenotype is preferred in disruptive selection?
BOTH extremes (select against the middle phenotype)
In disruptive selection what does the environment select for?
more than 1 phenotype
Reproductive isolation can occur in many ways - name them?
seasonal
mechanical
behavioural
Genetic drift can lead to ..
speciation
What does selective pressures do to allele frequencies?
changes them!
What is genetic drift?
This is when chance (not the environment) determines which organisms survive, reproduce and pass on their alleles
Genetic drift has a greater effect on which size population?
smaller populations
Genetic drift has less of an effect on which sized population?
larger populations
Describe Allopatric Speciation
Geographical isolation;
Separate gene pools
Variation due to mutation;
Different selection pressures;
Selection for advantageous allele;
Differential reproductive success / (selected) organisms survive and reproduce;
Leads to change in allele frequency;
Cannot produce fertile offspring
Describe Sympatric Speciation
Same location - Reproductive isolation;
Separate gene pools
Variation due to mutation;
Different selection pressures;
Selection for advantageous allele;
Differential reproductive success / (selected) organisms survive and reproduce;
Leads to change in allele frequency;
Cannot produce fertile offspring
