15677203
Description
Mind Map by Rosie Horwood, updated more than 1 year ago
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Created by Rosie Horwood
about 6 years ago
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|
10 - Variation and Evolution
- Variation
- Continuous
- e.g. height
- Normal distribution
curve
- Polygenic
- Range of phenotypes
- Environmental factors
have big influence
- e.g. height
- Discontinuous
- E.g. blood group
- Monogenic
- No intermediates
- Environmental factors
have little influence
- Bar chart
- Characteristics fit into
distinct groups
- E.g. blood group
- Causes
- Gene (point) mutations
- Crossing over in Prophase I
- Independent assortment in Metaphase I/II
- Random mating
- Random fusion
of gametes
- Epigenetic
modifications from
environmental factors
- Non-heritable variation from
environmental factors
- Gene (point) mutations
- Continuous
- Competition
- Intraspecific = members of the same
species compete for the same
resource
- Interspecific = members of different
species compete for the same
resource
- Intraspecific = members of the same
species compete for the same
resource
- Selection pressure
- = an environmental factor that can
alter the frequency of alleles in a
population, when it is limiting
- Natural selection = the increased chance
of survival and reproduction of
organisms with phenotypes suited to
their environment, enhancing the
transfer of favourable alleles from one
generation to the next
- Value of an allele depends
on the environment
- e.g. availability of nesting sites,
day length, overcrowding,
predation, temperature,
human impact
- = an environmental factor that can
alter the frequency of alleles in a
population, when it is limiting
- Population genetics
- Gene pool = All the alleles
present in a population at a
given time
- Allele frequency = The
frequency of an allele as a
proportion of all the alleles
of that gene in a gene pool
- Hardy-Weinberg
Equation
- p+q=1
- p^2+2pq+q^2=1
- p+q=1
- Gene pool = All the alleles
present in a population at a
given time
- Evolution and selection
- Evolution = A change in
the average phenotype of
a population
- Founder effect and genetic drift
- Genetic drift = Chance
variations in allele
frequencies in a
population
- Founder effect = The loss of genetic
variation in a new population
established by a very small number
of individuals from a larger
population
- Genetic drift = Chance
variations in allele
frequencies in a
population
- Natural selection
- Stabilising selection = the average
phenotype provide greater
advantage than either extreme
- Normal distribution
curve
- Normal distribution
curve
- Directional selection = an
extreme phenotype
becomes advantageous
- Disruptive selection =
average phenotype does
not provide an advantage
and is selected against, a
lower and higher value
are selected
- Stabilising selection = the average
phenotype provide greater
advantage than either extreme
- Evolution = A change in
the average phenotype of
a population
- Isolation and speciation
- Speciation = formation of
a new species
- Species = A group of
phenotypically similar
organisms that can
interbreed to produce
fertile offspring
- Reproductive isolation = The
presentation of reproduction and
gene flow between breeding groups
within a species
- Deme = Sub-group
within a
population that
breeds more often
- Pre-zygotic isolation
- Geographical
- Allopatric speciation = the evolution of
new species from demes isolated in
different geographical locations
- Allopatric speciation = the evolution of
new species from demes isolated in
different geographical locations
- = gametes are prevented from fusing, so a
zygote never forms
- Behavioural
- Mating rituals and
courtship displays
- Sympatric speciation = the
evolution of a new species
from demes sharing a
geographical location
- Mating rituals and
courtship displays
- Morphological
- Sympatric speciation
- Compatible/incompatible
genitalia
- Sympatric speciation
- Gametic
- e.g. germination/pollination
- e.g. germination/pollination
- Seasonal
- Geographical
- Post-zygotic isolation
- = gametes fuse and zygote
forms, is sterile
- Hybrid sterility
- hybrid = the offspring of a cross between members
of different species
- embryo develops but offspring is sterile, because
homologous pair cannot form at prophase I
- Hybrid no. chromosomes between that
of each parent
- hybrid = the offspring of a cross between members
of different species
- Hybrid inviability
- fertilisation occurs but
embryo does not form
- fertilisation occurs but
embryo does not form
- = gametes fuse and zygote
forms, is sterile
- Speciation = formation of
a new species
- Darwinian evolution
- 1. Organisms overproduce offspring, so
large genetic variation of genotypes in
population
- 2. Environmental changes bring new
selection pressures
- 3. Only individuals with beneficial
alleles have a selective advantage,
increasing their chance of survival
- 4. These individuals reproduce more
successfully than those without beneficial
alleles
- 5. Offspring likely to inherit beneficial alleles
- 6. Beneficial allele frequency increases
within the gene pool
- 6. Beneficial allele frequency increases
within the gene pool
- 5. Offspring likely to inherit beneficial alleles
- 4. These individuals reproduce more
successfully than those without beneficial
alleles
- 3. Only individuals with beneficial
alleles have a selective advantage,
increasing their chance of survival
- 2. Environmental changes bring new
selection pressures
- 1. Organisms overproduce offspring, so
large genetic variation of genotypes in
population
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