W4 Evolution I Flashcards
Rapid evolution of influenza virus by reassortment
Different flu strains infecting the same cell can swap parts of their genetic material.
H-haemagglutinin (bind to a cell)
N-neuraminidase (release from the cell > bud out)
The 2009 (and 2010) H1N1 strain contains alleles from human, avian and swine flu
Evolution
Accumulated, heritable changes in DNA w/in a population, over generations, giving rise to new species
New species arise from earlier species
Evolution is an observable fact. The process by which it has most likely occured, natural selection, is a theory
64 combinations for 20 AAs = redundancy
Observing evolution
Grow on a dish, each colonie = clone
Change every couple of days (new medium in flask)
12 colonies of E Coli from a single clone
Sub-culture every day, for 27 years
Freeze culture samples every 500 generations (75 days)
Over 63,500 generations have been observed
Test for ability to grow in citrate (anaerobic substrate) in the presence of oxygen
Evolution observed!
The ability to use citrate evolved after about 30,000 generations in one group in particular
Earlier generations from this same ancestral E coli were repeatedly able to evolve the ability to utilise citrate at about the same time
Will develop trate to use citrate
Citrate utilisation in E coli
Ancestors replicate (duplicate section of Citrate, RNK promoter) Make citrate utilising gene in presence of oxygen
Mutations in DNA are tolerated based on their effect
Sickle cell anaemia (SCA)
Mutation in beta-globin gene
Glu6Val
Mutant Hb molecules
Aggregate and form crystals when deoxygenated
Cells with characteristic “sickle” shape
Hg can’t fold properly so RBC get trapped in capillaries
SCA is autosomal recessive and causes early death
Correlates with regions of endemic malaria
Heterozygotes (carriers) have improved malaria survival rates
Lower parasitaemia
Fewer severe complications
Even though it’s a harmful mutation, it confers heterozygote advantage
How changes in genotype arise
Underlying all change is mutation/recombination of genetic material
Natural selection
Organisms better adapted to environment survive to produce more offspring
Genetic drift
Variation in relative frequency of different genotypes in small populations, due to chance. Does not rely on natural selection
Gene flow
Transfer of alleles (genes) from one population to another
Applied selection
Plant or animal breeding
Antibiotic, drug, pesticide resistance
Mistakes during DNA replication
Classification
Arranging taxa into an ordered, hierarchical system
Phylogeny
Determination of ancestral relationships of organisms and their evolutionary history
Greek phyl- refers to tribe; gen- refers to origin or descent
The fossil record
Older rock lies below more recent rock
Rock and organic material can be dated by measuring the decay of naturally occurring radioactive isotopes
Fossils usually form in sedimentary rock
Fossil dates can be bracketed by the age of surrounding igneous rock
Fossil formation
Surface erosion + sedimentation Sediment accumulates Pressure turns it into sedimentary rock Fossils in sedimentary rock Fossils older than igneous rock (rock from molten rock) sitting above them
Evidence for evolution from the fossil record
The order and age of organisms can be determined
Only simpler life forms are present in older rock
We find fossilised organisms that are no longer alive
Intermediate fossils are found (like Archeopteryx)
Half life
Period of time it takes for the amount of radioactivity to decrease by half of the original
Radiometric dating
Measuring the ratio of parent/daughter nuclides (as don’t know how much radioactivity you started with)
Relative ratio to parent:daughter
Requirements for radiometric dating
The rate of radioactive decay is constant
Not affected by temperature, pressure, chemicals, electrical or magnetic fields
Parent and daughter nuclides cannot leave or enter material after it is formed
No intrusion of other, later rock
No contamination
The Cambrian Explosion
The rapid appearance (and disappearance) of complex organisms in the fossil record (about 525Mya)
Burgess Shale (Canadian Rockies), Chengjiang Shales (Yunnan, China), Greenland, Sweden, Australia
First Arthropods, Trilobites, Echinoderms
Homology and analogy
Homology - similar by descent
Analogous - similar by function (convergent evolution)
Molecular analogy
Also known as molecular convergence
Same function of proteins with no structural identity (not related genetically)
e.g. the crystallins (lens proteins)
Many different transparent proteins in different species
All have/had other functions (in addition to being stable, transparent & refractive)
Different organisms use different proteins to make crystallins but get to the same place by using different molecules
Molecular homology
Molecular homology determined from amino acid or nucleic acid sequence:
Two genes from same organism (by duplication) – paralogs
Two genes from different organisms (common ancestor) – orthologs
Gene duplication in evolution:
Partition ancestral activity by regulatory mutation
Complementary functions
Non-overlapping functions
Can make changes to duplicate version
Hox genes
Hox genes bind DNA in a sequence-specific fashion and regulate the expression of adjacent/nearby genes
Confer positional identity along the Anterior-Posterior (cranio-caudal) axis
Drosophila Antennapedia mutants have legs instead of antennae
T marked = where thorax is so where legs are attached
Mutation so T marked now at head so this tells the organism to make legs instead of antenna
Evolution: the modern synthesis
Populations contain genetic variation that arises by random mutation and by recombination
Populations evolve by changes in gene frequency brought about by random genetic drift, gene flow, and especially by natural selection
Most adaptive genetic variants have individually slight phenotypic effects so that phenotypic changes are gradual (microevolution)
Diversification comes about by speciation, which normally entails the gradual evolution of reproductive isolation among populations
These processes, continued for sufficiently long, give rise to changes of such great magnitude as to warrant the designation of higher taxonomic levels (genera, families, etc.)
