W4 Evolution I

Question 1

Rapid evolution of influenza virus by reassortment

Answer 1

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

Question 2

Evolution

Answer 2

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

Question 3

Observing evolution

Answer 3

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

Question 4

Evolution observed!

Answer 4

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

Question 5

Citrate utilisation in E coli

Answer 5

Ancestors replicate (duplicate section of Citrate, RNK promoter)
Make citrate utilising gene in presence of oxygen

Question 6

Mutations in DNA are tolerated based on their effect

Answer 6

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

Question 7

SCA is autosomal recessive and causes early death

Answer 7

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

Question 8

How changes in genotype arise

Answer 8

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

Question 9

Classification

Answer 9

Arranging taxa into an ordered, hierarchical system

Question 10

Phylogeny

Answer 10

Determination of ancestral relationships of organisms and their evolutionary history

Greek phyl- refers to tribe; gen- refers to origin or descent

Question 11

The fossil record

Answer 11

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

Question 12

Fossil formation

Answer 12

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

Question 13

Evidence for evolution from the fossil record

Answer 13

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)

Question 14

Half life

Answer 14

Period of time it takes for the amount of radioactivity to decrease by half of the original

Question 15

Radiometric dating

Answer 15

Measuring the ratio of parent/daughter nuclides (as don’t know how much radioactivity you started with)
Relative ratio to parent:daughter

Question 16

Requirements for radiometric dating

Answer 16

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

Question 17

The Cambrian Explosion

Answer 17

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

Question 18

Homology and analogy

Answer 18

Homology - similar by descent

Analogous - similar by function (convergent evolution)

Question 19

Molecular analogy

Answer 19

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

Question 20

Molecular homology

Answer 20

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

Question 21

Hox genes

Answer 21

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

Question 22

Evolution: the modern synthesis

Answer 22

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.)