Population genetic basis of evolutionary change Flashcards
Two key figures in evolutionary science?
Charles Darwin (1809-1882) and Alfred Russel Wallace (1823-1913).
When was ‘On the Origin of Species’ published?
22nd November 1859.
What is Theodosius Dobzhansky’s famous quote?
Nothing makes sense in Biology, except in the light of Evolution.
What group of people criticise evolution as just a theory?
Creationists.
Definition of a theory?
A hypothesis that has been verified/ supported by facts.
What does consilience mean?
Different sources of evidence agree with one another.
Evolution the process definition?
The process of temporal change, by which organisms come to differ from their ancestors with respect to any heritable trait/ characteristic.
Definition of the term Heritable?
Characteristics passed on/ transmitted from parents to offspring - genetic and often expressed in phenotype.
What are the two processes of evolutionary change?
Transformation (anagenesis) and splitting/ branching (cladogenesis).
What is Anagenesis?
Between generation change within a single lineage (transformation).
What is Cladogenesis?
Division of a single lineage due to genetic divergence (splitting/branching).
What happens usually to the ancestral form in Anagenesis?
Disappears as entire species changes to a new form.
What results in further divergence during Cladogenesis?
Subsequent changes (anagenesis) occurs in both/ either sister lineages.
What can a division event result in?
Either 2 new lineages or just one new lineage in addition to original.
What are branched evolutionary histories known as?
Phylogenies.
What is the study/ reconstruction of phylogenies known as?
Phylogenetics.
What is Microevolution?
Evolution at the population level - within species evolution (ie intraspecific).
What are species comprised of?
One or more populations of many individuals.
Give an example of a process leading to speciation thats included in microevolution.
The production of new species.
Does speciation occur mainly through Cladogenesis or Anagenesis?
Cladogenesis.
What is Macroevolution?
Evolution at species level and above (ie interspecific).
What does Macroevolution involve?
Speciation events (splitting of lineages) and subsequent divergence of species and higher taxa.
What are characters?
Any measurable item on an organism.
What is a character state?
Alternative variants of a character.
What can characters also be referred to as?
Traits.
What is the genotype?
Genotypic traits - the information stored in the DNA of one individual.
What is the phenotype?
Phenotypic traits.
What three adjectives describe the genotypic characteristics of an organism?
Observable, measurable, detectable.
Where is DNA?
In nucleus (linear chromosomes), mitochondria (cytoplasmic circular), chloroplasts and kinetoplasts.
What were mitochondria derived from?
Endosymbiotic bacterium, formed first eukaryote cell.
What is junk DNA?
Sequences within introns of genes and those between genes.
How much of junk DNA in humans does have a function? Give an example.
80% - ie expression regulation (miRNA, snRNA…).
Why is junk DNA useful to evolutionary biologists?
Because true junk DNA is assumed not to be subject to natural selection.
How can there be genetic variation within individual organisms?
Nucleotide base sequences making up same gene may differ between individuals.
What does SNP stand for?
Single Nucleotide Polymorphism.
When nucleotide sequences differ at the same site (locus) on the paired chromosomes they are…?
Termed different alleles of the same gene and the locus is said to be polymorphic.
Can there be more than 2 alleles?
Yes many more.
Definition of genotype by evolutionary biologists?
The information stored in all of the genes of one individual.
Definition of genotype by population geneticists?
The combination of alleles at one or more studied/ examined loci in one individual.
What is genotype?
Information stored in DNA of one individual.
What is phenotype?
The observable/ measurable/ detectable characteristics of an organism.
What does phenotype comprise of?
External appearance, internal structures/tissues, intracellular structures, proteins/polypeptides.
Give an example of extended a phenotype?
Nests.
Why have scientists traditionally examined phenotype?
Easiest to observe/record/quantify, variation in most traits are partly genetically determined.
Give some non-genetic factors that some phenotypic variation may be due to.
Wear/ trauma, disease, somatic mutation.
What are soma cells?
Cells other than those which produce sperm and eggs.
What is heritable intra-population variation essential for?
Evolutionary change to occur - must be sufficient amount of variation.
Give an example of something that caused the lack of sufficient heritable trait variation.
Cloning by farmers (asexual reproduction leading to genetically identical parents).
Give two examples of pathogens of crop plants.
Potato Blight (phytopthora infestans) and black Sigatoka disease in bananas.
What made the banana disease problem worse?
Cultivation of only few varieties, propagated asexually, genetic variability in fungus.
What does continuous traits mean?
Intermediates exist between 2 extremes.
What does discontinuous traits mean?
No intermediates exist.
Characteristics of discontinuous phenotypic trait variation?
One or a few gene loci involved, usually only few alleles involved at such loci, allele-for-trait effect clearly evident in phenotype.
Characteristics of continuous phenotypic trait variation?
Many gene loci involved, many alleles involved, it is harder to discern the contribution of individual alleles to phenotype.
Continuous inheritance?
Polygenic.
Discontinuous inheritance?
Few loci, major effect.
Does environment play a role in continuous variation?
Often.
Does environment play a role in discontinuous variation?
Little effect.
What does sampling need to be like?
Representative, unbiased, random sample, large sample.
How do you assess continuous variation?
Measurement among individuals.
How do you assess discontinuous variation?
Scoring among individuals.
What does standard deviation measure?
Variance around the mean.
What does microevolution refer to?
How populations and gene pools change over time and in relative abundance of genotypes or phenotypes.
What is population genetics?
Processes that create genetic variation (mutation and recombination) and processes that remove genetic variation (everything else).
What is genetic drift?
Random changes in allele frequencies within a population.
What is selection?
Not random changes in allele frequencies - natural and artificial.
Does recombination cause genetic variation?
No, only mutations can but it can shuffle the genetic variation.
Characteristics of genetic drift?
Reproduction is random, bottleneck (random reduction).
What is inbreeding?
Mating between relatives.
What is linkage disequilibrium?
Non-random association between loci.
What happens when artificial selection is subjected to natural selection or its mimic?
Genetically determined phenotypic traits correlated with fitness typically alter in frequency within a population.
What kind of change is altering of traits in frequency within a population?
Directed change, in response to change in environmental variable.
Evolution of insecticide resistance?
Consider a genetic variant under insecticide free conditions, consider what happens when insecticides are applied.
What happens under natural insecticide free conditions?
Variant compared with normal form has shorter average life span, so leaves fewer progeny.
What happens to the less fit variant?
Remains rare in aphid populations over successive generations.
What is more likely to occur for a rare variant?
More likely to become extinct under insecticide free conditions due to random processes.
What happens when under insecticide conditions the variant is resistant?
Normal individuals die, less fit, variant longer average life span, more progeny.
What happens due to evolutionary change to the more fit variants?
Proportion within population as a whole will increase in next generation.
Characteristics of more fit variants?
Have selective advantage over normal form, unnatural selection, human caused.
What is adaptive evolutionary change?
Under natural conditions, genetic variant conferring higher fitness increases relative abundance within gene pools.
Three everyday examples of adaptive evolutionary change?
Insecticide resistance in head lice, warfarin resistance in rats, antibiotic resistance in bacteria.
What does artificial selection do?
Mimics natural selection, the breeder/ experimentar decides which trait has highest fitness.
Characteristics of artificial selection?
Results in adaptive evolution under artificial conditions, does not necessarily correspond to differential fitness under natural conditions.
What is the name for genes whose frequencies are not influenced by natural selection?
Selectively neutral genes.
What can change over time within a population?
Frequencies of variants of neutral traits - but it is undirected evolutionary change.
Why will neutral genes be subjected to selection?
They hitch hike with genes that have an adaptive function.
Are all neutral genes expressed in the phenotype?
No, some aren’t.
What can adaptive and neutral traits be subjected to?
Random changes in frequency within a population - can occur from random process.
What is pleiotropy?
Multiple phenotypic effects of an individual gene.
What can the effect of one phenotypic trait be like?
Adaptive (positive).
What can the effect of many phenotypic traits be like?
Neutral, deleterious or positive.
What can increased fitness in early life due to testosterone in males cause later on?
Prostate disorders.
What can pregnancy and lactation decreasing bone mineral density for females cause?
Osteoporosis.
What are the three kinds of selection?
Negative, positive, balancing.
What happens when selection pressures acting on an adaptive trait are completely eliminated?
The trait will be selectively neutral, until new predator arrives for example.
What may cause a particular genotype to produce a different phenotype?
The organisms particular environment - phenotypic expression if often environmentally determined.
What is the name for the other phenotypic expressions that are not beneficial due to environmental aspects?
Suboptimal.
What is adaptive phenotypic plasticity?
Each one of the different phenotypic expressions of genotype is beneficial.
Give an example of adaptive phenotypic plasticity.
Skin darkening and lightening in response to sun exposure - pale skin admits UV light for vitamin D production in winter, dark skin protects against too much UV in summer.
Is skin darkening a fixed plasticity?
No it is reversible but some forms of adaptive plasticity are fixed.
Give three types of constraint on evolutionary changes.
Insufficient genetic variation in gene pool, no selection pressures, constraints upon changing blue print of an organism.
Example how blue print constraints may arise?
Genome of organisms is coevolved, integrated assemblage of genes, cannot simply unravel to produce new structure.
What constraints mean insects have small body sizes?
Need to shed exoskeleton, if large their body would collapse at moult, and air carrying tubes would not work efficiently.
What is the name for the limit on insect body size?
Phylogenetic constraint (found within entire group of descendants, cannot be undone).
Is evolution goal directed?
No, no final model, adapted to prevailing conditions.
What is the Red Queen theory?
“It takes all the running you can do just to stay in the same place.”
