Topic 7 - Genetics, populations, evolution and ecosystems Flashcards
what is meant by the term genotype
the genetic constitution of an organism/ the genetic makeup of an organism, made up of alleles which determine a particular feature
what does a dihybrid cross determine
the genotypic and phenotypic combinations of offspring for two particular genes that are unlinked
how many gamete combinations will there be for 2 genes with 2 alleles each
4
define genetics
the study of inheritance
define phenotype
the features resulting from the expression of the genes and their interaction with the environment
define genome
the total genetic makeup of an organism
define gene
a section of DNA that codes for a particular protein
define dominant
alleles that always appear in the phenotype shown by capital letters
define recessive
alleles that are only expresed if both alleles of a pair are present, shown by lower case letters
define homozygous
two alleles of a pair are the same
define heterozygous
two alleles of a pair are different
define homozygous recessive
this describes an individual who has two recessive alleles of the same gene
define homozygous dominant
an individual who has two dominant alleles of the same gene
what is codominance
when both alleles are expressed in the phenotype
e.g. CRCR = Red flowers
CRCW = pink flowers
CWCW = white flowers
what do we call it when a lethal allele is expressed later in life
genetic disease
what is sex linked characteristics
when there are different genes for males and females
true or false
males never inherit their X chromosome from their mothers and pass it on to their daughters
false
males always inherit their X chromosome from their mothers and pass it on to their daughters
what is the chromosome for females
XX
what is the chromosome for males
XY
what is the phenotype ratio when two heterozygous parents are crossed
9:3:3:1
what is the phenotype ratio when heterozygous chromosome parents is crossed
3:1
using x and y what is the genotype for the description ‘homozygous dominant, homozygous dominant’
XXYY
what is an autosome
a chromosome that isn’t a sex chromosome
when does autosomal linkage of genes occur
when two genes are on the same chromosome
how could there be more genetic variation for gamates
crossing over due to weak linkage
finish the sentence:
the closer together the gene loci are on a chromosome…
the lower the chance of chiasma forming btwn them and separating them
why are the possible number of genotypes in the offspring reduced
when genes are on the same chromosome, they cannot be separated in meiosis I [independent assortment of homologous chromosomes], so two linked genes are passed into the gamete together and are inherited together
ratio for dihybrid unlinked vs autosomal linkage
dihybrid: 9:3:3:1
autosomal: 3:1
define epistasis
the genes at one locus interect with genes at another locus by masking or surpressing their expression
define allele
alternate version of a gene
what is the hardy-weinberg principle
a mathematical model which can be used to predict the allele frequency w/n a population
define species
a group or organisms with similar characteristics which can breed to produce fertile offspring and reproductively separated from other speicies
define population
group of organisms of the same species living in a particular area at a particular time
define gene pool
all alleles of the genes within a population at one time
define allele frequency
the proportion of an allele within the gene pool/how often an allele occurs in a popoulation (given as a % or number)
how does assumptions effect accuracy
it impedes it
what assumptions are made in the hardy-weinberg model
- large population
- no migration to introduce/remove alleles
- no mutations
- no selection favouring particular alleles
- mating is random [no selective breeding]
what is the equation for the hardy-weinberg equation
p^2+2pq+q^2 = 1
p + q = 1
where:
p = frequency of dominant allele
q = frequency of recessive allele
p^2 = the frequency of the homozygous dominant genotype
2pq = the frequency of the heterozygous genotype
q^2 = the frequency of the homozygous recessive genotype
what is genetic diversity
a measure of the number of different alleles in a population/all the different alleles available in the gene pool
what type of selection keeps variation around the mean
stabilising
what type of selection moves the variation away from the mean
directional
what is disruptive selection
when extreme phenotypes are favoured leading to an increase in alleles with distinct phenotypes
where does disruptive selection occur and what does this result in
in fluctuating environments where predation favours the middle range phenotype = two peaks at the extremes of the distribution
what can continued disruptive selection lead to
speciation (where new species are formed over time)
what causes allopatric speciatin
when populations are separated geographically leading to reproductive isolation
why does genetic variation always exist
random mutations
what could cause geographical isolation
natural disasters
what happens in allopatric speciation
- species are separated due to geographical isolation which results in an accumulation of different beneficial mutations = they become genetically different which means they cannot interbreed to produce fertile offspring, becoming 2 different species
why does sympatric speciation occur
populations become reproductively isolated due to differences in their behaviour
where does sympatric speciation occur
it occurs at a genetic level e.g. due to waking/sleeping patterns
how does sympatric speciation occur
the individuals do not see each other due to different changes in mutations, which means that they will not reproduce together = no gene flow = reproductively isolated populations will accumulate different mutations in their DNA which means they cannot interbreed to produce fertile offspring = two different species
define genetic drift
the random change of allele frequency due to only some of each generation reproducing
genetic drift always occurs from one generation to the next, what does continual and substantial genetic drift result in
evolution
what type of population is genetic drift found in
smaller ones
what is ecology
the study of relationships between orgnaisms and their environment - biotic and abiotic
what do ecologists study
the biosphere, land, air and water surrounding Earth
define abiotic
conditions that are physical, non-living parts of environment (e.g. temperature, light intensity, rainfall)
define biotic
conditions that invovle the living parts of the envrionment (e.g. competition, predation, disease)
define species
a group of organisms that can interbreed to produce fertile offspring
define population
all the organisms of one species in a habitat
define community
all the populations of different species living an area
define habitat
the place where an organism lives within an ecosystem
what is interspecific competition
competition for resources btwn members of different species
define intraspecific competition
competition for resources between members of the same species
what is population size
number of individuals
what is population density
number of individuals per unit area
what is population growth
change in number of individuals
what is population growth rate
change in number of individuals per unit time
what do we call the graph that is the most commonly found in population growth rate graphs
sigmoid or S-shaped
in signoid graphs, why does the population grow slowly at first
few to reproduce, may not find mate
in sigmoid graphs, what causes the exponential growth phase to end
lack of food/space, intraspecific competition, build-up of toxins, increase in disease
define carrying capacity
maximum population size which can be sustained. it varies due to abiotic factors and interactions between organisms
in sigmoid graphs, what are the factors which limit the size of a population known as
environmental resistance
what happens when the population size increases too rapidly
it may go above the carrying capacity of the environment
what is a population crash known as
boom and bust
what shape of the curve is known as for a boom and bust
J shaped
why would carrying capacity decrease
the environment is damaged by overpopulation
what factors limit population growth
density dependent factors: the higher the population density the greater the effect. normally biotic factors
density independent factors: have the same effect whatever the population density. normally abiotic factors
state two types of relationship btwn predators and their prey
seasonal relationships, larger efficient predators in a yearly cycle
describe a negative feedback loop in terms of predators and prey
when predator go up, preys go down, then there’s less food so predators go down
define ecological niche
how a species lives in relation to all the environmental factors that affect it.
what does a population niche refer to
its role in its ecosystem. e.g. feeding role in the food chain - predator, producer, parasite
what niches other than its feeding role could a population have
food, habitat, reproduction method, behaviour
how does different niches in ecosytems help us
they help use to understand the interactions btwn populations
do the members of the same population always have the same niche
yes and they are well adapted
what are specialists
species with narrow niches
can different specialists coexist in the same habitat
yes when they are not competing
what happens when different specialists coexist
leads to high diversity
what are generalists
species with broad niches e.g. common crow
in the same habitat, will generalists compete and how does this affect the diversity
generalists will compete, leading to low diversity
are generalists able to cope with a changing food supply
they can switch from one food to another or even one habitat to another
what is optimal niche
the ideal conditions for the individual to reproduce and maintain a viable population
when two addverse conditions are combined, what does this lead to
the organism cannot survive
what is a potential (fundamental) niche
the potential conditions under which the individual can survive
define autotroph
an organism that can convert abiotic sources of energy into energy stored in organic compounds
define succession
the change in a community over time due to changes in the abiotic environment
what kind of an environment might an ecosystem start with
extreme one e.g. bare rock or barren land
why might an ecosystem start with an extreme environment
- glacier retreating and depositing rock
- sand dunes forming by wind or sea
- volcanoes depositing lava
- slit and mud being deposited by reviers
- lakes or ponds being created by land subsidence
what does it mean for an ecosystem to be dynamic
they constantly change over time
which conditions change over time in succession
biotic and abiotic
define primary succession
the process that occurs when newly formed or newly exposed land is gradually colonised by an increasing number of species
summarise the process of primary succession
- pinoeer species can survive harsh conditions and colonise the area
- they can change abiotic factors of their environment e.g. decomposition adds nutrients to ground
- over time, this allows more complex organisms to survive
what is the climax community
the final stage of succession where the ecosystem is balanced and stable
when is the climax community reached
when the soil is rich enough to support large trees or shrubs and the environment is no longer changing
how might a species alter the environment that develops during succession
a species may improve the environment to make it more suitable for other species or, a species may worsen the environment by making it less suitable for other species
what happens as succession continues
community becomes more diverse with more complex food webs
what is the time period difference between primary and secondary succession
primary succession takes thousands of years, secondary takes decades
define sere
an alternative name for succession in a community
define primary succession
a succession sequence that occurs on land that has not had plants or soil in the past or has been completely cleared of these e.g. by volcanism usually bare rock
define abiotic factors
one of the non-living chemical or physical components of an ecosystem
define climax community
a community that has reached an equilibrium with the environment and no longer appears to be changing in composition
define pagioclimax
a course of succession which differs from the natural course of succession. often as a result of human activity but can also be due to natural cuases
define conservation
the active management of natural populations in order to rebuild numbers and ensure species survival
define colonising species
a species that is able to grow on bare land and rock, making nutrients available for species that establish later
define gap regeration
the regrowth of plants after a space in the canopy is opened, following the loss of a larger tree
define secondary succession
a succession sequence that takes place after a land clearance e.g. forest fire or landslide. it does not invovled the loss of seed and root stock
define deflected succession
a course of succession which differs from the natural course of succession e.g. as a result of human activity
define ecological succession
the progression from initial colonisation of a newly cleared area to a climax community
define pioneer community
the earliest community that becomes established on bare site
why doesn’t secondary succession require pioneer species
the soil is already developed and there is a seedbank
what is the impact of human activiity on succession
natural climaax isn’t reached due to farmland being weeded. this results in plagioclimax/artifical climax
state an ethical rreason why we conserve habitats
we should be able to coexsit with other species on earth and respect them
state an economic reason why we conserve habitats
the greater the diversity of organisms, the more substances could be produced, studied and may be valuable in the ftuure
state a cultural and aesthetic reason as to why we conserve habitats
ecosystems and wildlife provide us with enjoyment, interest and inspiration
when a climax community forms due to succession what happens
some of the species at earlier stages are no longer present, their hbiatats may disappear or may be out-competed
if a factor preventing a climax community was removed, what kind of succession would take place
secondary succession
what is a climax community also known as
climatic climax
give an example of a conservation conflict in the Uk
the conservation of hen harriers and commercial hunting of red grouse - hen harriers prey on red grouse chicks
define pioneer species
the first organisms to colonise an inhospitable substrate
as small plants die and decay in the soil, what increases
organic matter
define seral stage
a distinct community in the sucession
