Test 1 Flashcards
Two core Tenets of evolution
- Living things change over time
- adaptations have arisen through natural selection
what does evolution challenge?
the view of special creation
define special creation
the direct creation of all living things in effectively their present form
state 5 important conclusions about evolution verified by scientific study
- organisms on earth have changed through time
- changes are gradual, not instantaneous
- lineages split by speciation, resulting in the generation of biodiversity
- all species have a singular common ancestor
- adaptations result from natural selection
evidence for organisms changing through time
fossil records
why are changes in traits in organisms gradual and not instantaneous?
processes of evolution take different amounts of time, but always have to work with pre-existing variation, limiting the rate of change.
biodiversity and adaptation are the
products of evolution
describe speciation
process by which one species bifurcates into two which do not go back together. iterative rounds of speciation give exponential growth of this process.
give 2 definitions of biodiversity
- the diversity of life on earth
- the number and kinds of living organisms in a given area
give 2 definitions of adaption
- any trait that makes an organism better able to survive or reproduce in a given environment (noun)
- the evolutionary process that leads to the origin and maintenance of such traits, reproducing and surviving better in an environment (verb)
major areas of evolutionary study
- evolutionary history (i.e. patterns); reconstructing how life on earth happened
- evolutionary mechanisms (i.e. processes); what gave rise to the life that we see
microevolution
evolutionary patterns and processes observed within species
macroevolution
evolutionary patterns and processes observed among species
draw a diagram for macro and microevolution, as well as evolutionary history and mechanisms
goals of evolutionary history
identify and understand long term patterns in evolution, including common ancestry
evolutionary history in practice
uses comparative data from sub-disciplines of systematics, biogeography, palaeontology, morphology, development and molecular biology
give 2 alternative terms for an evolutionary tree
a phylogenetic tree = a phylogeny
what is the purpose for evolutionary trees?
to reflect ancestor-descendant links
name of split points in evolutionary trees
nodes
can trees with different sets of species represent the same common ancestors?
yes - this also depends on rotation of branches on the tree
goals of evolutionary mechanisms
- determine the particular processes responsible for evolutionary change
evolutionary mechanisms in practice
- uses experimental and comparative studies of the genetics and ecology of populations
- focuses primarily on the population level
state and describe the 4 approaches that are used to address scientific questions
- observational - describe and quantify
- theoretical - develop models (verbal, graphical, mathematical, computational)
- comparative - obtain same data from many species
- experimental - manipulate a system to address a specific hypothesis; requires an experimental design and statistical analysis
all good scientific theories have —- and the strongest studies use
testable and falsifiable hypotheses; more than one source of evidence
give 4 reasons as to why evolution is relevant?
- children’s questions/understanding life on earth
- medicine - mitigating effects of pathogens (eg variants of covid-19)
- agriculture
- how can we design strategies to avoid herbicide and insecticide resistant superweeds/super pests?
- what genes were important for crop evolution? - climate change - selection pressures will be applied
public doubts about evolution
- extremely recent scientific concept (165 years is a brief time frame)
- very personal implications: direct ramifications about who we are and where we came from
- violates literal interpretations of religious texts
open questions in Darwin’s time
- where do species come from?
- how can we explain complex adaptations (ie traits with clear/elaborate function for the survival and reproduction of organisms)?
Paley’s argument from Design
- Dominant view in European society - came from Natural Theology (branch of theology)
- on a walk and you find a watch, with perfect hands for minutes and hours
- they clearly have a specific function - somewhere on this planet must exist a ‘watchmaker’.
- trees are adapted to have very specific functions, they are perfectly designed for their life and function
- there has been a designer (ie God)
Jean Baptiste de Lamarck, 1744-1829
First to
- use term evolution
- provide a hypothesis for the causal mechanism (inheritance of acquired characters)
explain Lamarck’s example for the inheritance of acquired characters
- giraffe feeds on leaves
- will spend its whole life stretching its neck, allowing it to grow and reach further on the tree
- this trait is passed on
give a summary of the theory for the inheritance of acquired characteristics
Organisms can change their phenotype within their generation; having changed within the generation, they pass this to offspring
draw a diagram for Lamarck’s theory
who proved Lamarck wrong?
August Weismann’s Germplasm theory (1889)
- Inheritance only by germ cells (gametes); somatic cells do not function as agents of heredity, information only goes one way
- Thus genetic information cannot pass from soma to gametes and onto the next generation
- Modern interpretation in molecular terms: genetic information flows in one direction only: from DNA to protein but never in reverse
Therefore changes to the body cells would not be able to have an impact on gametes and be passed onto offspring
what experiments did Weismann do to prove his Germplasm theory?
got a bunch of mice, chopped off their tails, and bred them together - the offspring still had normal sized tails
describe Darwin and Wallace’s roles in developing the theory of evolution?
- Darwin developed first comprehensive theory of evolution
- Darwin and Wallace independently discovered the chief mechanism of evolution, Natural Selection
Two major theses of Darwin and Wallace’s theory of evolution
All organisms have descended with modification from a common ancestor: thus, living things changed over time
The process leading to evolution is natural selection operating on variation among individuals
describe the contents of Lyell’s book
- argued for uniformitarianism
- the forces and processes that shape the Earth’s surface are uniform through time (ie the forces we see today are the same as previous eons)
- present day geological processes can explain the history of the Earth Gradualism of erosion, earthquakes, volcanoes
Give the stages of Darwin’s development of this theory
- Exploration - voyage on HMS beagle around the world (1831-1836) as ship’s naturalist. Intellectual companion to Capt. Robert Fitzroy
- Gradualism - reads Lyell’s book ‘Principles of Geology’
- Species Vary - Variation patterns of Galapagos mockingbirds
- Struggle for existence - 1838, Darwin reads Malthus’ ‘An Essay on the principle of population’
implications of Lyell’s book for Darwin
- the notion of a dynamic rather than a static world
- changes build up gradually, by the same mechanisms today as in the past
implications of variation patterns of Galapagos mockingbirds for Darwin
- there are 4 similar species endemic to the islands descended from a South American mainland ancestor
- populations had very slightly different traits and were not constant
- Darwin thus began to doubt the fixity of species
Malthus’ essay on the principal of the population
there is a constant struggle for existence as populations could grow exponentially nut don’t due to limits on resources
two key dates for Darwin and Wallace
July 1858 - Linnean Society presentation of Darwin-Wallace paper
Nov 1859 - publication of 490 pg book on Origin of the Species
describe Darwin’s mechanism of Natural Selection (3)
- Variation: individual variation in a population
- Heredity: progeny resemble their parents Moree than unrelated individuals
- fitness: some forms are more successful at (surviving and) reproducing than others in a given environment (i.e. some are more fit than others)
Natural selection is heritable variation in fitness
state the 4 important elements of Darwin’s theory
- Evolution occurs primarily at the level of populations - individuals do not evolve
- Variation is not directed by the environment - individuals do not induce adaptive variation when needed
- Most fit type depends on the environment and changes from generation to generation
- ‘Survival of the fitter’ - evolution works with available variation, and will not necessarily achieve perfection
State the implications of Darwin’s theory
The concept of a changing universe; a phenomenon with no purpose
State the 4 sources of evidence for evolution:
- Geology
- Homology
- Biogeography
- Domestication
Lessons from Geology
- Earth is very old - this allows for an immense amount of time for biological evolution
- Intermediate forms - evidence for transitional fossils linking features of seemingly dissimilar relatives (eg ungulates and whales, or tetrapods and fish)
- Fossils in younger strata increasingly resemble modern species in the same region - older strata show increasing differences
Give an example of how discoveries of transitional fossils continue today
Tiktaalik roseae, discovered 2006
- has 2 legs and 2 fins
- nickname: fishapod
Define homology
Similarity of traits in two or more species that is due to inheritance from a common ancestor
Lessons from homology
Vestigial traits provide evidence of the evolutionary past:
- have no function/reduced function in extant organisms
- can only be explained by the presence of functional traits in ancestors, followed by evolutionary degredation
Homologous structures are ubiquitous across organisms:
- fundamental structural similarity reflects common ancestry
- homologous structures have evolved to serve very different functions
Define a vestigial structure
- features inherited from an ancestor, but reduced in morphology and function
- are homologous to functional structures in related species
Describe vestigial structures in Galapagos flightless cormorants compared to mainland cormorants
Mainland cormorants need to fly as they nest on trees; GF cormorants do not as they nest on rocks by the water. The wings of these two species, albeit varying in use, are homologous structures.
what is a vestigial structure in cave-dwelling morphs of Astynax Mexicanus?
they have evolved to lose their eyes as they do not need them
vestigial structures in humans
- ear muscles
- appendix
- tailbone
- goosebumps
why is the presence of vestigial structures significant?
- organismal features are consistent with modifications of pre-existing structures
- this would not be expected if each organism was individually optimally designed
describe homology in genes
- approximately 500 genes are shared across all forms of life
- there is a strong, shared constraint for genes involved in basic cellular function (eg transcription/translation)
Lessons from Biogeography
Remote islands biotas:
- have continental affinities
- are dominated by good colonists
- have locally-differentiated species
biogeographically isolated regions:
- have species adapted to niches unusual for their group
- harbor endemic radiations of species that are convergent with radiations elsewhere
3 main points of evidence from biogeography
- geographically close organisms resemble each other
- different groups of organisms adapt to similar environments in different parts of the world
- geographically isolated regions have unusual organisms
use Australia as an example of a location with an interesting Biogeography
- although a continent, Australia is also an island
- distinct flora and fauna with high endemism and many unique adaptations
- australia has endemic radiations of species that are ecologically convergent with those of other continents
what is Australia’s biological uniqueness a result of?
its long history of isolation from other land masses
give a summary of evidence from domestication
Heritable variation can be selected on, leading to dramatic changes over generations
define genotype
the genetic constitution of an organism
- defined in relation to a particular gene or gene combinations
- eg Aa, Bb
define phenotype
feature of the organism as observed
- used when discussing a trait of an organism that varies
- eg size, fur colour, mRNA expression level
define genome
the entirety of an organism’s DNA
- includes genes and non-coding regions
state 3 sources of genetic variation
- mutation
- independent assortment
- recombination
define a mutation
a stable change in the DNA sequence
how often do mutations occur?
at a low rate
- mutation rate varies in ways that are partially predictable
what are the different possible effects of mutations on fitness?
- neutral (won’t matter for the fitness of the organism)
- deleterious (weakly detrimental up to lethal)
- beneficial
state the 4 main characteristics of mutation
- mutation is an inevitable phenomenon, despite cellular mechanisms to correct errors during DNA replication
- mutation is not directed toward an outcome by the organism or by the environment
- it is random with respect to effects on fitness
- it is not ‘summoned’ to make things better - rate depends on the type of mutation, and can also vary among genes
- the environment can affect the mutation rate (eg mutagens, high temp)
what are the 4 types of mutation?
- point mutations (a simple substitution of a nucleotide)
- insertions/deletions (‘indels’) - adding/removing a nucleotide
- changes in repeat number
- chromosomal rearrangements (eg inversions)
describe a mutation involving a change in repeat number
- when there is a repeated motif (eg ATG) within the gene, the motif may accidentally be added/removed an extra time
- the repeated motif makes it harder for the replicative machinery to replicate
describe an example of a chromosomal rearrangement
inversions:
- flipping of the nucleotide sequence
- occurs when there is a double break in DNA strand; when enzymes try to put the two strands back together, it is hard to know which one was forward and which one was backwards
give an example of a method that can be used to identify a new mutation?
a trio study:
- two parents (reproducing organisms) are selected
- their genome and the genome of their offspring is sequenced
what is the rate of new mutation in humans?
per base pair of DNA: 16 in every billion nucleotides each generation
per individual genome (two copies of our 3 billion base pair genome): approx. 96 new mutations per zygote
for the entire human population (8 billion): every base pair in the genome mutated about 126 times over per generation
why do some mutations not lead to amino acid changes?
we have more codons than amino acids - so sometimes mutations don’t make a difference to the amino acid sequence (= silent substitution)
give an animal example of how single mutations can cause profound effects on traits
- Antp Hox gene mutations in Drosophila
- results in an extra pair of wings, for example, or a set of legs, instead of antennae, growing from the fly’s head
describe G6DP deficiency in humans?
Glucose-6-phosphate dehydrogenase
most common enzyme deficiency in humans
- causes severe anemia
- also protects against malaria
- 2 amino acid replacement mutations in the coding sequence of G6PD are associated with disease allele (A-)
what are polymorphisms?
- A gene is said to be polymorphic if more than one allele occupies that gene’s locus within a population.
- each allele must also occur in the population at a rate of at least 1% to generally be considered polymorphic.
what are allozymes?
Alloenzymes are variant forms of an enzyme which differ structurally but not functionally from other allozymes coded for by different alleles at the same locus.
give a flow chart for how mutations in G6PD lead to genetic variation
DNA (polymorphisms) -> proteins (allozymes) -> phenotype (polyphenisms)
define independent assortment
the alleles of two (or more) different genes get sorted into gametes independently of one another.
how does independent assortment in segregation during meiosis generate diversity?
- allows different combinations of parental chromosomes
- 2^n, where n=sets of chromosomes
how can we tell if a mutation has increased or decreased fitness from a fitness distribution bar chart?
if the mutation leads to a fitness less than 1 (which is the fitness of the ancestor) then they are detrimental
describe how recombination during meiosis (metaphase) further contributes to variation
there is synapsis of bivalents, leading to crossing over at chiasmata and recombinant chromosomes.
how did scientists believe that heredity worked before Mendel?
performatifs (1700s):
- spermists/ovists believed only one parent contributed to inheritance
theory of blending inheritance (1800s)
- postulated that factors from both parents mix together irreversibly
what is the problem with blending inheritance for evolution by natural selection?
there would be no way for a beneficial mutation to increase in frequency across generations
describe Mendel’s experiment with diagrams
- hybrid cross of pure-breeding lines (yellow and green)
- self fertilised (all yellow)
- offspring were 3/4 yellow and 1/4 green
state the key conclusions from Mendel’s pea experiments
- inheritance is determined by discrete particles, genes
- each diploid organism carries two copies (alleles) of each gene.
- alleles can exhibit dominance/recessivity
- gametes contain only one allele per gene - gametes fuse to make offspring
- sperm/pollen fuses with egg/ovule - offspring inherit one gamete from each parent at random
- one allele per gene at random from each parent
describe phenotypic polymorphisms with simple mendelian genetic causes
- common in nature
- direct correspondence between trait and its genetic basis
- easy to track selection and evolution
what are the two types of genetic variation?
discrete variation:
- mendelian genetics
- genes of major effect, dominance, and recessiveness
- involves a spread of alleles and a change in allele frequency
continuous variation
- quantitative genetics
- many genes each with alleles of small effect, important environmental effects
- selection response as change in average trait value
define discrete variation
Discrete variation refers to traits with a finite number of phenotypes, often controlled by single genes
define continuous variation
Continuous variation, on the other hand, displays an infinite number of phenotypes across a continuum and is usually polygenic.
how is the phenotype of a quantitative trait established?
- often affected by many factors
- complex polygenic inheritance
AND - environmental factors
define partial dominance
a form of Gene interaction in which both alleles of a gene at a locus are partially expressed, often resulting in an intermediate or different phenotype.
