unit 4 aos 2 Flashcards
gene pool
the total genetic diversity (alleles) in a population
> greater genetic diversity = larger gene pool
genetic diversity
- the variation in alleles in a population
- occurs due to sexual reproduction through independent assortment and genetic recombination
allele frequency
- allele = alternative form of a gene
- calculated by counting all the specific alleles and dividing by total number of alleles
mutations
- random, unpredictable change to the DNA of an organism
- source of new alleles, causing diversity in the same species
- can be spontaneous or induced
causes of changing allele frequencies
- environmental selection pressures (natural selection)
- genetic drift
- gene flow
- mutations
gene flow
- movement of alleles from one population to another, due to individuals entering or leaving a population. Results in changes in the allele frequency of a gene pool and therefore the genetic diversity
genetic drift
a change in the allele frequency of a population due to random chance events
two types:
- bottleneck effect
- founder effect
bottleneck effect
- change in allele frequency due to a cataclysmic event, causing a sudden drop in population (near extinction)
> natural disasters, disease, human intervention
causes populations to undergo new selection pressures - population then grows in numbers again, but allele frequency has changed as only few individuals survived, lowering genetic diversity
> larger impact on smaller populations
founder effect
small group of individuals/ alleles is isolated from a larger population, causing them to undergo new selection pressures and form a new species
> larger impact on smaller populations
environmental selection pressures
- environmental factors that affects the survival and reproduction of an organism
- only organisms with favourable characteristics will survive, leading to low genetic diversity or the creation of a new species
natural selection
- the influence of environmental pressures on allele frequency. organisms that have more favourable characteristics and are better adapted to their environment are more likely to survive and reproduce
adaptations
allow organisms to survive & reproduce within a changing environment
- structural: physical, eg. anteaters long tongue
- physiological: involves the function of organs/ systems that affect its biological fitness, eg. chameleon changing colours
- behavioural: affect how an organism behaves in itss enviro, allows it to thrive in its ecosystem, eg. male birds sing to attract females
consequences of changing allele frequencies
- mutations can introduce new alleles to a population & increase genetic diversity
- loss of alleles can lead to a decline in genetic diversity and possibly the creation of a new species
selective breeding/ artificial selection
- humans select organisms to breed which carry what we deem to be desirable traits
- causes a change in the allele frequency of the population in order to produce individuals suited to human use
- decreases genetic diversity in a population by eliminating undesirable alleles from the gene pool
- low genetic diversity can make populations susceptible to disease
> selective breeding has increased dairy cows milk yield of 3750L per cow per year, to 7445L per
steps of selective breeding
- select desired trait
- breed 2 organisms with desired trait
- select best offspring
- repeat for many generations
> takes a long period of time
antigenic drift
an accumulation of mutations over time which results in changes to the antigens on the virus’ surface
antigenic shift
an abrupt change in the genome of the virus due to swapping genetic material while in the host cell
> requires 2 viruses at once
antibiotic resistance
random mutations can occur to bacteria which give them the innate ability to tolerate an antibiotic
> these may not be killed by antibiotics, and can then reproduce, and horizontal gene transfer can occur, giving plasmids to other bacteria & creating a population of bacteria that all have resistance
> natural selection resulting in antibiotic resistant bacteria
treating against pathogens
- vaccinations can give immunity, but can be made redundant if viruses mutate
- antibiotics treat against bacteria, it is important to take the full course as some bacteria have mutated to be antibiotic resistant, and can survive & reproduce if full course of antibiotics isnt taken
the fossil record
evidence of evolution, shows how organisms change from simple to complex over time
fossil
preserved, hardened remains or traces of organisms within sedimentary rock
types of fossils
- impression fossil/ mold: shape of the organism left on the rock after it has decayed
- mineralised fossil/ petrified: minerals replace the material of the organism
- trace fossil: record of the organisms activities, eg. footprints, burrows
- mummified fossil: preserved in something other than rock, reduces decay
index fossils
- abundant, distinctive fossils used as reference to determine the age of unknown fossils, have existed for a short period of time & have a known age
- when these same fossils are found in other sedimentary layers, they can be used to date those layers
> eg. trilobites, arthropods
transitional fossils
fossil has both primitive and derived trait, provide evidence that an ancestral species evolved
> divergent evolution
> eg. lobe finned fish transitioned from fish to amphibian
faunal (fossil) succession
fossils found in sedimentary rock succeed one another in a predictable order
> compared via index fossils found within rock layers
relative dating
- used to compare different fossils
- if an unknown fossil is found in between 2 known layers, it can be assumed to be in between their age
- bottom layers of sedimentary rock are older than those at the top
- stratigraphy: the study of the age of strata (layers of sedimentary rock
absolute dating
- more precise estimate of age than relative dating, includes:
- radiometric dating
- thermoluminescence
- electron spin resonance
radiometric dating
- type of absolute dating
- carbon-14 decays into nitrogen-14.
- carbon-14 stops being replenished in the body when an organism dies, and nitrogen-14 builds up
- 14C decays into 14N at a known rate, so the levels of each can be compared to determine how long ago the organism died
- works on fossils up to 60,000 years old
speciation
- species: group of organisms that are genetically similar enough to interbreed and produce fertile offspring
- speciation: creation of a new species
types of speciation:
> genetic isolation
> allopatric speciation
> sympatric speciation
genetic isolation
- occurs when alleles are no longer exchanged between populations
- can be prezygotic or postzygotic
electron spin resonance
- used to date limestone, coal, molluscs and eggshells
- smashes electrons against the fossil
- used for objects upto 300,000 years old
- looks at calcium-carbonate impurities
thermoluminescence
- used to date objects that have been previously heated
> eg. pottery, furnaces, archaic tools - more light = older age
- can destroy the object
- works for objects up to 500,000 years old
prezygotic isolation
- prevention of mating
- prezygotic = before egg fertilisation
> geological/ spatial: physical land barrier between a population
> ecological: occupy diff ecological niches
> temporal: timing of mating seasons don’t align
> behavioural: diff mating rituals in animals (eg. mating calls)
> structural: sexual organs are different or don’t fit- physically can’t mate
> gamete mortality: egg & sperm fail to fertilise
> sexual selection: how organisms choose mates (desirable traits)
postzygotic isolation
- prevent a zygote of 2 diff species from developing into a fertile adult
> hybrid inviability- 2 different speacies have created a zygote but it’s not fretile due to unmatched chromosomes- (cant do mitosis)
hybrid viability
- inviability: 2 genetically similar organisms that are different species create a zygote, creates a hybrid
> hybrid is infertile due to parents having diff amounts of chromosomes
> eg. zebra has 64, donkey has 62, so zonkey has 63 > cant be split in meiosis - partially viable: lives for a while, then dies
- sterile: viable but infertile
allopatric speciation
occurs due to different selection pressures & genetic drift that occurs once a population has been split through geographic isolation, resulting in 2 different populations
> eg. Darwins finches in the galapagos islands lived in different selection pressures due to different environmental conditions, causing them to vary in size, beak shapes and food
> shows relationship between selection pressures and morphology (structure)
adaptive radiation
- form of allopatric speciation
- refers to the rapid evolution in one place of one species into many
sympatric speciation
- the evolution of a new species from a common ancestor due to reproductive isolation while both continue to inhabit the same area
- common in plants, uncommon in animals
- occurs due to a mutation making an organism polyploidy (having more than 2 sets of homologous chromosomes), making them unable to reproduce with the original population, creating a new species
Lord Howe island Howea palms - sympatric speciation
- howea belmoreana (nutrient rich) and howea forsteriana (nutrient poor) both inhabit lord howe island and diverged from a common ancestor long after the island was formed
- the two palms now grow in different nutrient level soils, causing them to have different flowering times and become reproductively isolated. develop diff mutatrions over time & evolve into different species
structural morphology
looking at the similarities and differences in the structure of different species
evidence of evolution from homologous structures
- features of organisms that have the same fundamental structures, but different functions, they show evidence of common ancestry
- eg. mammals, birds and reptiles have the same arrangement of bones in their forelimbs which all serve different functions, suggesting that these structures were inherited from a common ancestor
evidence of evolution from analogous features
- features of organisms that have the same function, but different structures, they are evidence of convergent evolution
- the similarities are not due to common ancestry
vestigial structure
- structures that have no apparent function in a species which resemble functional structures found in its ancestor and other species
> evidence that the organism evolved from an ancestor that needed that feature
> eg. whale has pelvic bone, humans have muscles in their ears like those dogs have to move their ears
molecular homology used to determine relatedness
- looking at similarities in DNA and amino acid sequences between organisms to determine how related they are
> more differences = less related
comparing DNA sequences to determine relatedness
comparing DNA sequences: looks at differences in nucleotides to compare each differences in organisms
> species with fewer differences in their nucleotide base sequences have diverged from a common ancestor more recently, because there’s less time for mutations to occur in their genome
comparing amino acid sequences to determine relatedness
comparing different proteins (polypeptide chains) between species
> more differences = less related, diverged a along time ago and vice versa
molecular clock
- shows how long it takes for a mutation to occur
- uses the mutation rate of genes to determine how different two organisms are, as well as when they diverged
- look at eg in chriso notes
mitochondrial DNA (mtDNA)
- slow mutating segment of DNA which can be used to track long term changes in humans
- passed from mother to offspring, allows you to track maternal lineage and therefore evolution
phylogenetic trees
- branching diagrams that show evolutionary relationships between groups of organisms
- root: start, shows common ancestor
- branch: each line of tree
- node: a divergent event- splitting of branches
- leaf: end of branch, shows taxa or species
> sister taxa = grouped together, closely related species - clade: a common ancestor and its descendents, particular group in a tree
types of phylogenetic trees
- phylogram: contains a scale of time
- cladogram: doesn’t have a scale
shared characteristics of primates
- forward facing eyes
- opposable thumbs
- flat fingernails & sensitive fingertips
- sexual dimorphism
- form complex social groups
- mammary glands
important groups of primates
- monkeys
- hominoids
> gibbons
> hominids
–> great apes
> hominins (humans and other homos)
trends in human evolution
Australopithecus –> H.habilis–> … H.neanderthalensis–> H.sapien
trends include:
- larger cranial capacity (brain size) over time
> increased skull volume = greater intelligence
- limb structure
> longer legs in proportion to arms, due to bipedalism
> locking knees
> greater angle at femur & shin bones join at an angle to support centre of mass & bipedalism
> pelvis has gotten smaller and flatter
classification of humans
kingdom: animalia
phylum: chordata
class: mammalia
order: primates
family: hominidae
Genus: Homo (capitalised)
species: sapiens
“King Phylum Can Only Find Green Socks”
multiregional theory
-all spontaneously mutated into homo sapiens (unlikely)
out of Africa theory
~300,000 years ago, homo sapiens arose in Africa
- attempted to leave after 150,000 years
- successfully migrated out of Africa (~70,000 years) and colonised rest of world
-more likely theory
how is the out of Africa theory supported by mtDNA
- there is more genetic diversity between people in Africa compared to other people in the world ( more diversity in people in Africa than comparing someone from Australia and Sweden etc)
-(founder effect)- little part of pop left africa , not representative of african population/pool (low genetic diversity), - few mutations/mutates predictably, so it can be used to track lineage
- no recombination
-errors aren’t repaired
interpreting the fossil record
- can be difficult as it is incomplete and is often revised with new discoveries
- discovery of new species such as H. florensis fossils and denisovans bones found challenge previously held hypotheses of fossil record
evidence for interbreeding between homo sapiens and homo neanderthalensis
- evidence that H.sapiens and H.neanderthalensis interbred and produced fertile offspring
> this is because all humans except those from africa have some neandethal DNA - however they are seperate species according to paleontology.
evidence of new putative homo species
migration of aboriginal and torres strait islander
~ 65,000 ya H.sapiens arrived via land bridge
-came from asia
- split from population in Papua New Guinea/Indonesia
-took ~9000 years to spread across Australia
-fossil evidence may be hard to obtain as its seen as potentially disrespectful to use ancestral remains
connection to country and place (from bens notes)
- due to the long occupation of australia by the indigenous pop the community has a strong connection to land
- their connection to country involves a reciporical relo in which people sustain and manage the land through culture, ceremonies and care the land provides them
