Topic 10 Flashcards
natural variation
- mutations create new alleles
- different allele combinations- different phenotype
- environment may influence phenotype
population
group of organisms of one species that interbreed and live in same area at same time
monomorphism
- populations that show one form of characteristic
- all members of population are identical in that particular trait
- no variation exists in population
polymorphism
- show 2 or more variants for particular characteristic
- polymorphic traits show continuous or discontinuous variation
monogenic traits
- variation that occurs due to different alleles of single gene
- when gene has two alleles and dominant or recessive-only two variations
- when gene has two alleles and are codominant - only three variations
discontinuous variation
- when members of population can be classified into few distinct non-overlapping classes
- monogenic traits show discontinuous variation
polygenic traits
variation caused by two or more genes at different loci
-genes often called polygenes-expression often influenced by environmental factors
continuous variation
- cannot be classified into few distinct groups- show variety of phenotypes
- polygenic traits show continuous variation
difference in variation between asexual and sexual organisms
asexual- produced by mitosis and genetically identical to parent, variation occurs via mutations or environment
advantages- no mate needs to be found and large number of offspring can be produced at short time
disadvantages- in changing environment, entire population are susceptible- due to genetically identical
sexual- organisms produced as a result of fusion of egg and sperm- develops into genetically different individual, variation due to allele combinations, recombination, independent assortment, random gamete fusion, mutations or environment
advantages- in changing environment- varied population ensures some individuals with suitable characteristics will survive
disadvantages- mate needs to be found, signal may alert predators, takes time
gene pool
sum total of genetic information present in population at any one time
allele frequencies tend to stay constant
- allele frequencies in populations remain constant over many generations
- theorised by hardy and weinberg
- mathematically describes frequency of alleles in sexually reproducing species
- no matter how many times alleles are segregated and recombined- allele frequency remains constant
conditions of hardy winberg principle
large populations random matings- all matings equally fertile producing equal numbers of viable offspring no migration no selection pressure no mutation
what is permanent change in allele frequencies in population
microevolution
change agents in population
selection (natural and artificial) gene flow (emigration and immigration) chance events- genetic drift, bottleneck effect, founder effect
lamarcks view
organism changes when it needs to
- structures used are acquired then developed- can be passed on to offspring
- other non used structures disappear
darwins view
one phenotype has greater chance of surviving in particular environment
- organism survive and reproduce with similar characteristics
- characteristic frequency increases in population
adaptation
-characteristic that suits organism to its way of life and environment in which it lives in-aids survival
selective advantage
describes phenotype with higher fitness value
selective agent
environmental factor that acts on particular phenotypes, causing it to have reduced fitness value in comparison to other phenotypes
random mating
-situation where all possible mating are equally likely to occur
complete selection
occurs when any organism with given phenotype cannot reproduce because death before reproductive age or sterility
partial selection
occurs when matings involving that phenotype produce average fewer viable, fertile offspring, relative to other matings
natural selection
process where agents of selection act differentially with no human intervention on various phenotypes in members of population
differential reproduction
one inherited variety in population produces more viable offspring than other varieties-makes greater contribution of alleles to gene pool of next generation
how does natural selection act on phenotypes
- eliminates/reduces reproductive success of individuals with poorly suited phenotypes-alleles become less frequent
- enhances survival/reproductive success of individuals with well suited phenotypes- alleles become more common
natural selection explanation
Within a population of (state organism) there was variation in the characteristics (state characteristics). This is a genetically determined characteristic that can be passed on to their offspring.
-When the environment changed (state the change in the environment) OR in an environment (state environment), the (state the advantageous phenotype) characteristic resulted in the organisms that possessed it having a greater chance of survival. (Explain why)
The (relevant environmental factor) was a selection pressure/selective agent so that organisms with the advantageous characteristics had a greater fitness value as they were more likely to survive and reproduce.
-The organisms that survive to reproduce will produce offspring that are likely to possess (state the advantageous phenotype) due to the alleles inherited from their parents. This will also have a greater chance of survival in a (state the particular environment).
-Over a number of generations, the frequency of (state the advantageous phenotype) will increase until the entire population will display it. Thus a change in the species has occurred as a population has adapted to its environment. Provided that the selection pressure remains the same.
gene flow
movement of genes into or out of population
- movement of alleles between populations via migration-occurs rapidly
- occurs when frequencies of alleles change rue to introduction or loss of alleles
- smaller population greater impact of gene flow
- larger populations have more stable allele frequencies-greater reservoir of alleles
genetic drift
- direction of change is unpredictable
- change in next-gen allele frequencies is random
- population can become well adapted or less well adapted
- doesn’t favour one phenotype
- greater impact on small populations
- occurs due to random fertilisation
bottleneck effect
- comes into operation when population size is reduced for at least one generation
- caused by random events
- only small sample of individuals remain in population- may or not represent population
- can lead to random shift of allele frequencies among survivors
- severely limited genetic variation may be outcome
- small population can be affected by inbreeding- result is little genetic variation
founder effect
- small number individuals may migrate or become isolated from population
- colonising/founder population will likely have small, non-representative sample of alleles from parent population gene pool
- due to isolation- will not inherit other alleles- less phenotypes
- as result- evolution of founder population may occur differently from parent population
speciation
process of formation of new species
- change agents cause phenotype frequency to change
- if population becomes separated from one another- may be subjected to different selection pressures- exist in different environmental conditions
- overtime, each population may become different from each other- subspecies formed
- subspecies can still interbreed and produce viable offspring
- if prolonged separation occurs, and continue to evolve in different directions- new species forms
species
members of same sexually reproducing species are able to reproduce under natural conditions to produce fertile viable offspring
pre mating isolation mechanisms
time of day
space-habitat locations
behaviour-sexual readiness
anatomy-physical differences
post mating
gamete incompatibility
zygote failed development
zygote develops embryo, not beyond
sterility- organism is born but can’t reproduce
phyletic evolution
ancestral species progressively changes over time- recognised as new species
branching evolution- a population of one species splits and evolves into new species
allopatric speciation
- speciation occurs when populations become geographically isolated
- subjected to different natural selection pressures
- establish reproductive isolation
allopatric speciation steps
Some individuals from a species may become geographically separated into two or more populations by isolating mechanisms
gene flow between the populations does not occur and so no interbreeding occurs between the two populations.
Members in these isolated populations will be exposed to:
Different selective agents due to different environmental conditions.
The effect of chance events may produce different changes.
Different mutations may occur.
Gene pool of each population becomes more different over time.
Different phenotypes will be selected for in these isolated populations, therefore different phenotypes will increase in frequency in the different populations over many generations.
Over a period of time, members of each population may become increasingly different from one another so that races or sub-species result.
Over a longer period of time, the two sub-species become so different that they can no longer reproduce to produce viable offspring.
They have become reproductively isolated.
mutations
-source of new alleles/mew chromosomal arrangements
-mutations are chance events
-if new mutation to allele gives survival advantage over other individuals, will contribute to inherited gene pool in population
-point mutation-single base substitution
-frame shift- insertion or deletion of base pair
block mutations- changes to segments of chromosomes
types of block mutations
duplication
deletion
translocation
inversion
causes of mutations
random- error in DNA replication, occurence during meiosis, genes mutate at different rates
mutagenic factors- radiation, microorganisms, poisons, alcohol and diet
selective breeding
- artificial selection
- only organisms with desired phenotype are chosen to reproduce
effects of selective breeding on genetic fitness
- manipulates gene pool
- chosen characteristics- may not be helpful to organism survival, usually selected against under natural selection
- can lose genetic diversity
- may cause reduced genetic fitness
