U4A2 Flashcards
gene pool
complete set of alleles present within a particular population.
allele frequency
proportion of certain alleles in a gene pool, calculated by frequency divided by total.
factors that can influence gene pools
mutations
environmental selection pressures
genetic drift
gene flow
artificial selection pressures
mutation
permanent changes to DNA sequences
2 categories of mutations
point mutations: change to a single nucleotide in a gene
block mutations: change to larger sections of DNA
4 categories of point mutations
silent mutations: no effect on amino acid sequence due to genetic code’s degenerate nature
missense mutations: substitute mutations that code for a different amino acid. (sickle cell anaemia)
nonsense mutations: substitute mutations that prematurely end translation of gene’s mRNA
frameshift mutations: alter reading frame of all following nucleotides.
4 categories of block mutations
deletion: removal of DNA section
duplication: replication and lengthening of DNA section
inversion: reversal of DNA section
translocation: switching of DNA sections on different chromosomes.
environmental selection pressures
factors in the environment that impact an organism’s ability to survive and reproduce
natural selection
mechanism through which organisms that are better adapted to their environment have increased chance of surviving and passing on alleles.
4 basic conditions that facilitate natural selection
variation: genetic diversity leads to phenotypic differences.
selection pressure: ESP impacts survivability of oragnisms in a population.
selection advantage: ESP aids survivability of certain organisms
heritability: advantageous trait must be heritable, over time allele frequency will increase.
darwin’s 4 observations
- there is phenotypic variation within species
- offspring tend to inherit the traits of their parents
- species produce more offspring than required to replace themselves
- there is struggle to survive
darwin’s 2 inferences
- individuals whose traits increase survivability leave more offspring than other individuals
- the unequal chance of reproduction will lead to accumulation of favourable traits in the population
genetic drift
changes to a population’s allele frequencies due to sudden and random events
2 types of genetic drift
- bottleneck effect
- founder effect
bottleneck effect
large portion of a population is wiped out by a random event, decreasing population size and lowering genetic diversity.
founder effect
small unrepresentative sample of individuals seperate from larger population to colonise new region and start a new population.
2 risks of reducing genetic diversity
- inbreeding
- lower adaptive potential
gene flow
introduction/removal of alleles between populations through either migration or inbreeding.
2 types of migration
immigration + emigration
speciation
process in which populations genetically diverge until they become distinct species.
isolating mechanisms
pre- and post-reproductive isolating mechanisms prevent species from interbreeding.
5 pre-reproductive isolating mechanisms
- geographical
- ecological
- temporal
- behavioural
- structural
geographical isolating mechanism
separation by barriers
ecological isolating mechanisms
separation by ecological niches or habitats
temporal isolating mechanisms
time when individuals are ready to breed differs
behavioural isolating mechanisms
mating behaviours differ
structural isolating mechanisms
physical characteristics prevent breeding
3 post-reproductive isolating mechanisms
- gamete mortality
- zygote mortality
- hybrid sterility
gamete mortality isolating mechanism
sperm unable to penetrate ovum
zygote mortality isolating mechanism
zygote is not viable
hybrid sterility isolating mechanism
offspring is viable but infertile
2 types of speciation
allopatric
sympatric
allopatric speciation
formation of a new species as a result of a geographical barrier. barriers isolate populations, preventing gene flow.
sympatric speciation
formation of a new species located in the same geographical location.
selective breeding
changing a population’s gene pool due to humans altering the breeding behaviour of animals/plants to develop a specific trait. (artificial selection)
3 requirements for selective breeding
- variation: genetic diversity leads to phenotypic variation
- selection pressure: human intervention places artificial selection pressure, only allowing desirable traits to breed
- heritability: selected trait must be heritable
4 bacterial mechanisms against antibiotics developed by mutations
- impermeability (modified cell wall protein)
- inactivation (addition of phosphate group to antibiotic, reducing ability to fight antibiotics)
- pumping out (increasing active efflux of drugs)
- modification (changing protein shape)
3 factors that contribute to the formation of antibiotic-resistant bacteria
- inappropriate compliance with a treatment plan
- inappropriate use of antibiotics
- widespread use of antibiotics
antigenic drift
small and gradual changes to genes encoding for surface antigens. mutations accumulate, forming a new virus subtype.
antigenic shift
sudden and significant changes to genes encoding for surface antigens. 2+ different strains combine when coninfecting the same host, forming a new subtype via viral recombination.
fossil record
information derived from fossils arranged chronologically.
process of fossilisation
- organism remnants are covered by sediment.
- over time, sediment layers build + compact layer by layer until pressure cements them together to form sedimentary rock.
- inside the rock, the fossilised remains may be a permineralised, mould or cast fossil.
permineralised fossils
fossil formed when mineral-rich groundwater deposits minerals into organic material.
mould fossil
fossil formed when a living thing decomposes underneath sediment, creating a cavity in the shape of the dead organism.
cast fossil
fossil formed when a mould fossil is filled with sediment
trace fossil
indirect evidence of an organism’s existence
5 conditions that increase the likelihood of fossilisation
- physical protection from scavengers
- rapid sediment accumulation
- constant cool temperatures
- low oxygen availability
- low light exposure
relative dating
comparing its position to other fossils/rock in surrounding rock layers
law of fossil succession in relative dating
fossils closer to the surface must be younger than those below them.
geographical timelines in relative dating
scientists are able to assign each layer to a particular period of time based on the law of fossil succession.
index fossils
help determine the relative age of a new fossil. index fossils have been dated using radiometric methods. they must be distinctive, abundant, distributed worldwide, and existed for a short period of time.
transitional fossils
exhibit traits common to both an ancestors and its descendants.
absolute dating
known half-lifes of different radioisoptopes can be used to measure the absolute age of a fossil.
3 principles of absolute dating
- radioisotopes are unstable elements that will break down over time into a more stable product.
- on average, the rate of radioisotope breakdown is constant and can be modelled.
- half-life describes the amount of time before half of the radioisotope mass is broken down into predictable and stable products.
2 common radiometric dating techniques
- carbon-14 to nitrogen-15. half-life is 5730 years. dating period is 1000-50,000 years
- potassium-40 to argon-40. half-life is 1.3 bya. dating period is 100,000+ years.
3 principles of radiocarbon dating
- all living things contain carbon. carbon exists as a ratio of two isotopes: 12C and 14C.
- when the organism dies, its 14C will decay as it is radioactive. levels of 12C remain the same. the ratio of the two isotopes change.
- at any time, scientists can measure the amount of 14C in the fossil to determine how long ago it died. 14C:12C ratio is compared to atmospheric ratio.
3 categories of structural morphology
- homologous structures
- analogous structures
- vestigial structures
homologous structures
physical features that may look and function very differently from each other but can be shown to have derived from a common ancestor. example of divergent evolution.
analogous structures
physical structures that serve similar biological functions but are not derived from a common ancestor. example of convergent evolution.
divergent evolution
process in which a common ancestor evolves into 2+ descendant species
convergent evolution
process in which distantly related species evolve similar traits over time due to similar selection pressures
vestigial structures
physical structures that once served a pupose for an organism’s ancestors but, due to changing selection pressures, have lose their original function and are no longer required for survival.
2 categories of molecular homology
- amino acid sequences
- DNA sequences
amino acid sequences in molecular homology
used to determine how related different organisms are by analysing proteins from conserved genes found in a number of different species.
- haemoglobin
- cytochrome C
haemoglobin use in molecular homology
can be used to assess the degree of relatedness between species.
carries oxygen around the body.
composed of 4 polypeptie chains, 146 amino acids.
cytochrome C use in molecular homology
can be used to assess the degree of relatedness between species.
enzyme made by mitochondrial DNA.
composed of 104 amino acids.
dna sequences in molecular homology
can be used to determine the relatedness between different organisms similar to amino acid sequences.
compare by looking at the order of bases at corresponding gene regions.
mitochondrial dna in molecular homology
circular, maternally inherited DNA found in mitochondria. composed of 17,000 nucleotides and 37 genes.
phylogenetic trees
diagrams that show the evolutionary relationships between different species.
3 uses of phylogenetic trees
- displaying timeline of lineages
- displaying relatedness between taxa
- displaying shared characteristics of different taxa
4 components of phylogenetic tree
- root (line at the origin. represents earliest common ancestor.)
- branch (each line on phylogenetic tree.)
- node (point where branches split; divergence between taxa.)
- leaf (end of a branch.)
taxon
unit of classification in which related organisms are classified.
8 categories in the taxonomic classification system
kingdom, phylum, subphylum, class, order, family, genus, species.
human taxonomic classification
kingdom: animalia
phylum: chordata
subphylum: vertebrata
class: mammalia
order: primates
family: hominidae
genus: homo
species: homo sapien
key characteristics of primates
3D colour vision
large cranium relative to body weight, flexible spines, rotational hips and shoulders, prehensile hands/feet with opposible digit, receptors in fingertips.
categories in hominoidea category
- great apes: orangutans, chimps, gorillas, humans.
- lesser apes: gibbons.
key characteristics of hominoids
shorter spine, increased brain size, molar teeth in Y5 pattern, longerarms than legs, lack of tail, broader rib cage + pelvis.
examples of hominins
homo sapiens, homo neanderthalensis, homo erectus, australopithecines.
key characteristics of hominins
large brain size relative to body size.
cerebrum became more folded, enhanced cognitive ability.
bipedalism
pros and cons of having larger brain
benefits:
- lower predation vulnerability
- shared mothering
- stable food production
negatives:
- higher energy needs
- higher complexity of childbirth
- larger diet
reasons the human fossil record is incomplete
- not all individuals die in fossilisation-promoting conditions
- rock layers and fossils may erode and disappear over time
- many rock layers are still inaccessible to paleontologists
evidence for human/neanderthal interbreeding
- nuclear DNA studies show 1-4% of the human genome is identical to Neanderthal DNA.
- 100,000-year-old DNA from Neanderthal fossils contained significant amounts of human DNA
homo denisova
interbred species occuring 15-44kya.
homo luzonesis
small-bodied hominin ancestor that lived 50-67kya.
2 evolutionary hypotheses
- out-of-africa hypothesis
- multi-regional hypothesis
out-of-africa hypothesis
suggests homo sapiens evolved in Africa 200kya before emigrating and replacing existing hominin species in Europe and Asia.
evidence supporting out-of-Africa hypothesis
- repeated large-scale analysis of mtDNA shows our lineages can be traced to a common ancestor living in Africa
- modern-day humans show very little genetic diversity
multi-regional hypothesis
suggests evolution of modern humans was an ongoing process across all world regions.
evidence supporting multi-regional hypothesis
morphological clades
