classification, variation and evolution Flashcards
the different types of variation and their descriptions
Continuous: controlled by a number of genes character shows a gradation from one extreme to the other
Discontinuous: controlled by a single gene
no intermediate forms
characteristics are clear cut and easy to tell apart
Heritable variation
results from genetic changes due to sexual reproduction
three processes that result in heritable variation
- what do these processes generate
the mixing of two different parental genotypes in cross-fertilization
the random assortment of homologous chromosomes in metaphase 1
crossing over between homologous chromosomes during prophase 1
- new allele combinations
what generates novel long-lasting variations
only mutations
non-heritable variation
environmental influences that determine phenotypic variation
what causes non-heritable variation in humans
diet
exercise….etc
what causes non-heritable variation in plants
temperature
light
availability of inorganic ions
what happens if organisms of identical genotypes are subject to different environmental influences
they show considerable variety
interspecific competition
what is this type of competition illustrated by
competition between individuals of different species
predator-prey relationships
intra-specific competition
this type of competition is the basis of the origin of species by?
competition between individuals of the same species
Natural Selection
if a population reproduces sexually, then it has a large number of variations. true or false
true
gene pool
all the alleles of all the genes of all the individuals in a population at any one time
allele frequency
a measure of the relative frequency of an allele on a genetic locus in a population
under which circumstances does the gene pool remain stable
if the environment is stable
what happens in a population if there is a sudden change of the environment
some phenotypes become more advantageous than others
they are therefore selected for whilst the disadvantaged phenotypes will be selected against
therefore the gene pool changes over time and certain alleles become more frequent than others
selection pressures
external factors that affect the frequency of certain alleles within a gene pool
selection
the process by which organisms better adapted to their environment survives and breed, while those less well-adapted fail to do so.
after selection, the better-adapted organisms are …………………… to pass on their ……………………….. to ………………………………
more likely
characteristics
succeeding generations
give four examples of selective agents
supply of food
breeding sites
climate
human impact
what does the selection pressure determine
the frequency of an allele in a gene pool
what is the hardy-weinberg equation for predicting genotype frequencies?
where p^2 represents?
q^2 represents?
2pq represents?
p^2+2pq+q^2= 1
the frequency of homozygous dominant alleles
the frequency of homozygous recessive alleles
the frequency of heterozygote alleles
the hardy-weinberg principle suggests that the frequency of dominant and recessive alleles will remain constant in a population if five conditions are true.
what are the 5 conditions?
there is a large population
the population is isolated, so there is no emigration and immigration
there is no selection for or against any phenotype
there is random mating throughout the population
there are no new mutations
will there be evolution if the conditions under which the hardy-weinberg principles apply do not change?
no there would not
natural selection
refers to when organisms which are better adapted to their environments are likely to survive and reproduce to produce fertile offspring
processes leading to natural selection
variation due to new (random) mutations
overproduction (the production of a large number of offsprings)
struggle for survival, whereby only the fittest survive
the individuals that survive reproduce, passing on their characteristics to their offsprings
the offspring therefore gain a selective advantage
over many generations, individuals that once belonged to the same species may give rise to two different groups, which are significantly distinct to belong to separate species
species
a group of similar individuals that are able to interbreed and produce fertile offspring, and it is reproductively isolated from other such groups
speciation
features of behaviour, morphology or genetics which serve to prevent breeding between species
name factors that can cause changes in the equilibrium of a gene pool
genetic drift
mutations
natural selection
founder effect
when a population is isolated on an island or a new habitat, the founder members are a small sample of the original population
how does founder effect cause a genetic drift
the founder members may have very different allele frequencies to the original population by chance
so if the population size remains small, they may undergo a genetic drift
bottleneck effect
effects resulting from a disaster that drastically reduces population size, like earthquakes and volcanic eruptions
types of speciation and their descriptions
2 types
allopatric: speciation resulting from geographical features
sympatric: speciation resulting from habitat changes, morphology, breeding mechanisms and behavioural changes
what happens to the population in allopatric speciation
the population becomes physically split in separate demes
adaptive radiation
this is where present day species have all descended from a common ancestor and have over time occupied different niches via natural selection
reproductive isolation
when organisms inhabiting the same area become reproductively isolated into two groups where there are no physical barriers
give 4 barriers to breeding
temporal or seasonal isolation
behavioural isolation
mechanical isolation
gamete isolation
hybrid sterility
hybrid unviability
seasonal or temporal isolation
when the breeding season or time of activity of two closely related populations don’t exactly correspond
behavioural isolation
where traits develop which are very specific to closely related species, thereby preventing them from mating
morphology
when closely related species are unable to physically mate due to incompatibility between their genitals
hybrid sterility
this is when the set of chromosomes from each parent are different and can therefore not pair up in meiosis 1 and produce gametes
give an example of a case of hybrid sterility
horses and donkeys reproducing to produce sterile mules
horses have 64 chromosomes and donkeys have 62, their offspring has 63 chromosomes
mules are sterile because their parental chromosomes cannot pair up in prophase 1 of meiosis 1, because they are not homologous
so meiosis in fails and gametes are not produced
how do plants deal with the problem of hybrid sterility
plants can reproduce asexually to produce a colony of sterile hybrids
occasionally, the hybrids undergo mutations to become polyploid, meaning they double their chromosome set
now their chromosomes can pair up in prophase 1 of meiosis, making them a new species of fertile, mutant hybrids
biodiversity
the number of species and the number of individuals of each species in a given environment
the three main reasons for which biodiversity can vary
succession
natural selection
human influence
ecological succession
the observed process of change in the species structure of an ecological community over time
adaptive radiation
this occurs when a species colonises an area with several niches available
adaptation
organisms specialising to suit the environment they live in
why do organisms adapt
so that they are uniquely able to exploit their own niche
thereby ensuring that their niche is different enough to that of others, to avoid competition
behavioural adaptation
these are actions by the organism which help them to survive or reproduce
physiological adaptation
give example of a physiological adaptation
these are internal workings within the organism which helps it to survive or reproduce
fish, birds and whales are able to drink salt water, whereas humans cannot
a low level of diversity from the simpson’s diversity index suggests?
dominance by just one or few species
that a change in one species is more likely to affect the others
the community is unstable and could be able to withstand change
what are the measures taken to ensure the data is accurate when calculating the species density of a grassland
do a random sampling
use a reliable number of quadrats
identification of species
standardisation of techniques
sure that the species are not larger than the quadrat
a gene’s position on a chromosome
locus
polymorphism
it results from multiple alleles for the same gene
