natural selection and inheritance Flashcards
a genotype is…
genetic constitution of an organism
a phenotype is…
expression of the genotype and its interaction with the environment
alleles are…
variants of a different gene (eye colours), occur due to mutations in a gene that occur at different positions in the gene.
in diploids, chromosomes form pairs called…
homologous chromosomes
alleles at specific locus can be homozygous if they are…
the same type of allele or heterozygous if both alleles are different
an allele is dominant if…
it’s expressed in the phenotype of a heterozygote, so only 1 copy is needed for expression
an allele is recessive if…
it is not expressed in the phenotype of a heterozygote, so 2 copies have to be present for expression
codominant alleles are…
when both alleles are equally dominant and equally expressed in the phenotype
a monohybrid cross is when…
1.if you cross a homozygous dominant with a homozygous recessive, 100% of offspring would be heterozygous carriers
2. if you cross 2 heterozygous carriers then 25% of offspring would be homozygous dominant (unaffected), 50% would be heterozygous (unaffected) and 25% would be homozygous recessive (affected)
3:1 of unaffected to affected phenotypes
test crosses are…
used to determine an unknown genotype, the unknown genotypes crosses with homozygous recessive individual
if all offspring have dominant phenotype, then unknown genotype is homozygous dominant
if half of the offspring have the recessive phenotype, then unknown genotype is heterozygous.
homozygous is when…
you inherit one type of a particular gene
heterozygous is when…
you inherit two different types of a particular gene.
a dihybrid cross is when…
you inherit 2 different genes
autosomal linkage is…
2 or more genes located on the same autosome
less likely to be separated during crossing over so inherited together
offspring more likely to resemble parental genotype
sex linkage is…
gene is on the X chromosome
males more likely to have recessive conditions because they only require one copy of the sex-linked recessive allele for expression
inherited from mother
epistasis is…
interaction between 2 genes where one gene masks the expression of the other gene in the phenotype
the suppressing gene is called the epistatic gene+ the suppressed gene is called the hypostatic gene (can be dominant or recessive)
dominant= expression of dominant allele
recessive= 2 copies required to mask expression of hypostatic gene
9:3:4
chi-squared test
determines probability of unexpected result being due to chance or being significant
based off of null hypothesis= any difference that occurs between observed and expected results is due to chance
X^2= (sum of)[(O-E)^2]/E
a population is when…
group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed.
species can exist as one or more populations
a gene pool is…
total no. of genes of every individual in an interbreeding population
allele frequency is…
how often an allele occurs in a populayion
Hardy-Weinberg principal
predicts allele frequencies will not change from generation to generation
Hardy-Weinberg assumptions are…
mating is random
no natural selection occurs
no mutation
no gene flow/genetic drift
population size in infinite
Hardy-Weinberg calculation…
p^2 + 2pq + q^2 = 1
p= frequency of one (usually dominant) allele
q= frequency of other allele
2pq= frequency of heterozygote
p^2= frequency of homozygous dominant
q^2= frequency of homozygous recessive
variation is…
phenotype variation within every population due to a combination of genetic and environmental factors
primary source of genetic variation is…
due to mutation- produces different alleles
another source of genetic variation is…
random fertilisation of gametes, independent segregation and crossing over
environmental sources of genetic variation is…
disease, predation and competition
some effects of selection of allele frequencies is…
not all individuals in a population can survive due to environmental factors
organisms with phenotypes providing a selection advantage are more likely to produce more offspring + pass of favourable alleles
directional selection is…
selection favours one extreme phenotype
results in increased of favoured allele over time
stabilising selection is…
selection favours average phenotype/allele
disruptive selection is…
favours both extreme phenotypes/alleles but at different times due to environmental factors
speciation is…
evolution of new species from existing ones
arises when genetic differences due to selection leaf to an inability of members of the population to interbreed + produce fertile offspring
allopatric speciation is…
when the population becomes geographically separated so;
unable to reproduce due to physical barrier, separate populations have different environments/ selection pressures so accumulate different beneficial mutations over time to survive which leads to differential reproductive success, changes allele frequency
allopatric speciation leads to…
2 populations becoming so genetically different that they can’t reproduce to produce fertile offspring, now classed as different species.
sympatric speciation is…
population become reproductively isolated due to differences in behaviour so;
random mutation could influence reproductive behaviour, individuals will not reproduce together
sympatric speciation leads to…
DNA becoming different so individuals are no longer able to reproduce offspring, classed as 2 different species
genetic drift is…
change in allele frequency within a population between generations
genetic drift leads to…
continual leads to evolution]has larger effect in small population as allele frequency changes have larger impact
evolution occurs more rapidly in small populations
community is…
all populations of different species in the same area at the same time
ecosystem is…
community and non-living components of an environment
niche is…
organisms’ role within the ecosystem, each species occupies own niche
biotic factors are…
impact of interactions between organisms
abiotic factors are…
non-living factors in an ecosystem
carrying capacity is…
max population size an ecosystem can support
abiotic factors affecting population size are…
pH, soil quality, temperature, O2 levels, CO2 levels, light intensity
plants an animals become adapted to these factors by natural selection
species diversity and population size is larger when abiotic factors are less extreme
biotic factors affecting population size are…
interspecific competition
intraspecific competition
interspecific competition (biotic factors affecting population size)…
members of different species compete for the same resources which are limited
better-adapted individuals are more likely to survive and reproduce
intraspecific competition (biotic factors affecting population size)…
members of different species compete for the same resources which are limited
better-adapted individuals are more likely to survive and reproduce
estimating population size techniques…
quadrants
belt transects
mark-release-recapture
quadrant method is…
used to sample slow or non-mobile organisms
1. place 2 tape measures at right angles to create a gridded area to take sample from
2. use a random no. generator to generate coordinates to take sample from
3. place a quadrat on coordinate and either count abundance of species or calculate percentage cover
4. repeat at least 30 times- representative
can be measured using frequency (how many squares it’s in), density (every individual counted), percentage cover ( estimate percent of whole quadrat covered by species) (total count/ no. squares counted) x total no. of squares in habitat
belt transect method is…
used instead of random sampling (show change)
1. tape measure placed through a non-uniform ecosystem
2. quadrat placed at intervals along the transect to measure the impact of changes in the environment
mark-release-recapture method is…
used for mobile organisms
1. animals trapped + marked with substance non-toxic, weather-resistant, and not impacted by predation + reproduction
2. released and left to distribute themsleves in population
3. recaptured a few days later and a 2nd sample is taken, repeated at least 10 times
population size= size of 1st samplexsize of 2nd sample/ no. of marked recapture
assumes there is enough time for organisms to distribyte themselves and no migration
primary succession is…
a change in an ecological community over time
primary succession steps are…
- pioneer species (lichen) colonises bare rock or sand
- pioneer species adapted to survive harsh abiotic conditions
- moss + smaller plants can now survive, and they further increase depth + nutrient density of the soil as they die
- this continues, larger plants can survive + further change the environment
- each new species may change the environment in a way that the previous species can no longer survive as they have become lout-competed
- changes result is less hostile environment + increase biodiversity
- final stage of succession is a climax community
conservation of habitat is…
to conserve habitats, succession is often managed
climax community is prevented, so there is a wider variety of habitats and therefore a higher species diversity
provides conflict between human needs + conservation
different types of primary succession are…
lithosere= on bare rock
psammosere= on sand dunes
hydrosere= on a body of fresh water
halosere= on a muddy shore (salt marsh)
