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Population Genetics and Evolution (Evolution and the Origin of Life image…
Population Genetics and Evolution
Concepts
evolution is extremely slow and occurs over many generations :timer_clock:
geological evolution was discovered once explorers became aware of such changes that occur over long periods of time
such observations were not made till after the renaissance and scientific method was used :<3:
evolution is gradual conversion of one species into another/ new species :star:
occurs by natural selection :crossed_swords:
mutations can help benefit or be detrimental to species survival
once more beneficial alleles are common, can lead to evolutio of species
Charles Darwin and Alfred Russel Wallace independently discover natural selection around 1859 :!:
gave a rational explanation for many different species and their interaction with environment
this discovery came about the same time as genes and chromosomes, and cell theory were introduced
Population Genetics
genetic recombination of 2 different genotypes are important in population genetics
crossing over also increases genetic diversity in populations :red_flag:
total number of alleles in all the sex cells of all individuals of population constitutes the gene pool :check:
sexual reproduction does not alone change the gene pool as ratios of individuals gametes do not cross or change
Factors that Cause the Gene Pool to Change
Natural selection
2 conditions must be met for natural selection
the population must produce more offspring than can possible grow and survive to maturity in that habitat :red_flag:
condition valid for almost all plants on earth
limited resources, pathogens, predators and competitors all lead to a plants survival and adaptability in habitat
progeny must differ from each other in their allele type :star:
if all are similar, all will be affected the same by conditions in the environment
natural selection will not occur when all allele frequencies are the same
when genetic diversity exists among individuals. differential survival can occur :check:
competition of resources will also cause genetic adaptation and act as a selective force
an allele can appear that allows plant to absorb resources better and thus out competing the surrounding plants allowing survival
if a plant contains a allele that makes them resistant to fungi, it will fare way better during a fungal outbreak
after the outbreak the resistant allele will be more prevalent in the gene pool :green_cross:
natural selection can also work if outbreak did not kill the non resistant plants as they will produce less seeds than the healthy ones
natural selection is the most significant factor causing gene pool changes "survival of the fittest" :<3:
individual in this category are most adapted to their environment
natural selection refers to the differential survival among organism of different phenotypes
a resistant allele must exist before say a fungal outbreak occurs and does not occur because of it s
natural selection can cause a population to become more resistant to disease if a resistant allele is already present :check:
a population or species evolves not an individual :red_flag:
an individual also cannot become more adapted in its lifetime, only the population over generations
natural selection only acts on preexisting alleles and does not cause mutations :star:
natural selection is not always caused by external factors :red_flag:
can come from within as a plant could have allele that produces more chloroplasts and in turn synthesizes more resources
Artificial selection
can cause ornamental plants to flower more abundantly or for longer times
can also alter flower color, size, and hardiness causing them to be unrecognizable form the original groups :no_entry:
often carried out in conjunction with artificial mutation :star:
plants will be exposed to chemicals or gamma rays to cause a mutation and increase number of new alleles
desired phenotypes will be kept and breeded again
process in which humans purposefully change allele frequency in a gene pool :warning:
including selective breeding and of crops and domesticated animals
plant breeders will often combine wild varieties with cultivated ones when they have desirable traits :<3:
can cause the alleles for the entire gene pool to be entirely artificially selected :open_mouth:
Accidents
for large plants, natural disasters/ accidents are examples of selective forces :check:
less adapted plants will struggle and dies but not affect strong plants
example includes the drifting of Antarctica and to the south pole to cause the elimination of its abundant plant life due to freezing temperatures :thermometer:
Accidents can be large or small in scale
a small event could wipe out a local population that has an adapted allele but are confined in a small region
accidents are events in which an organism cannot adapt :checkered_flag:
can cause the elimination of entire gene pools including mutations and beneficial genes
can also affect a particular gene which will alter allele and its frequency
Factors that are not part of natural selection
intention
planning
humans and other primates are the only organisms to have intent and purpose that also affect our voluntary actions :star:
purpose
voluntary decision making
mutations
all genomes are subject to mutagenic factors causing mutations to occur continually :warning:
frequencies of existing alleles can decrease and cause an increase of new alleles
frequency of a mutation can be small in but its presence should not be overlooked :red_flag:
the significance of the mutation is dependent on the size of the population :explode:
population genetics deals with abundance of different alleles within population :star:
and the manner of abundance of a particular allele's increase, decrease, or same rate of occurrence :star: over time
Multiple Selection Pressures
a mutation that can be beneficial to the population could also be eliminated by various other factors
if survival occurs however it can benefit the population and increase in frequency
however, it can produce disadvantageous side effects that can do more harm than the initial benefit
can come from a multitude of different ways both external and internal :check:
Situations in which Natural Selection Does Not Operate
competition does not occur when there is enough resources in a given environment :check:
places like this include plowed fields, road sides, recently burnt fields, or flooded areas rich in nutrients
natural selection can occur however if a newly cultivated area is in a shaded forest and in this case plants not use to direct sunlight will undergo natural selection :!!:
does not occur when population is identical genetically
Speciation
Divergent speciation is when some populations of a species evole into new population while a second population remains the same :star:
Abiological Reproductive Barriers
original species is physically divided into two or more populations that cannot interbreed; if speciation occurs is called
allopatric/ geographic speciation :black_flag:
these include mountains, rivers, deserts, and even valleys :warning:
any physical, nonliving feature that prevents two populations from exchanging genes is an abiological reproductive barrier :red_flag:
divergent evolution can result in a subpopulation becomes a new species or two subspecies becoming 2 different species :checkered_flag:
if alleles that arise in one part of the range so not reach individuals in another part, the two regions are reproductively isolated :star:
Biological Reproductive barriers
differences on flower color, shape or fragrance can cause a barrier if species is pollinated by discriminating pollinator :!:
when two groups become reproductively isolated even though they grow together= sympatric speciation
is any biological phenomenon that prevents successful gene flow, called biological reproductive barrier :red_flag:
evolutionary changes in pollinators can act as barriers :green_cross:
prezygotic isolation mechanism occurs when pollination does not move from plant to plant, act even before zygote is formed
environmental diversity can also play a role as a barrier
plants can be spread throughout range that can have huge differences in quality causing different alleles to be produced
genomes thus, will be very different and iis called postzygotic internal isolation barriers as the two subpopulations must be considered different :forbidden:
one of the earliest postzygotic barriers to arise is hybrid sterility :check:
when two population that are continuously differentaiting from each other, the zygote that gets produced dies early in development
this is called hybrid inviability :star:
after internal isolation barriers are established, evolutionary divergences happens rapidly
occurs when two different populations interbreed and produce a seed that is viable but infertile for reproduction :star:
Adaptive Radiation
occurs when species enters new habitat with little or no competition
all offspring greatly resemble the first, founder individuals because initial gene pool is extremely small
if one seed is the founder, the original gene pool consists of its two sets of alleles
becasue of small population, accidents and other factors can affect gene pool creating a genetic drift :check:
occurs when island is far away form mainland and seeds are rare in occurrence
is special case of divergence in which species rapidly diverges into many new species in short amount of time :star:
Phyletic speciation is when one species gradually becomes so changed that it must be considered a new species :star:
gene flow is the movement of alleles physically through space and occurs in ma different ways
Seed Disposal
seeds can be carried by wind, floods, stream flows :star:
can take plant to island and start populating it
spiny or gummy seeds can stick to animal fur, very important for dispersal. migratory animals the most important to said animals :check:
frutis and seeds of some plants fall close to parent but many have
long-distance dispersal mechanisms
Vegetative Propagation
if the various mechanisms are sufficient to enable alleles that arise in one part of species range to travel to all other parts,
the species will remain relatively homogenous even as entire species evolves into new species :check:
alleles that arise at various geographic sites ultimately come together by gene flow :check:
if species produces small. mobile pieces that reproduce vegetatively, they can contribute to gene flow :star:
Pollen transfer
wind distributed can cover great distances, include ragweed, conifers, grasses :tornado:
if new allele is carried by grain, it can move to very distant plants
if sperm cells fertilize egg, new seed is formed whose embryo contains new allele :star:
Grain carries one full haploid genome, and all alleles of the plant :check:
speciation is when natural selection has caused a new species to occur :star:
new species considered a new species if they are cross breeding with another organism and do not produce fertile offspring :check:
breeding naturally= same species, if manual breeding does not result in interbreeding= different species
occurs in two fundamental ways, phyletic and divergent speciation
Convergent Evolution
as consequence, two may evolve to the point that the strongly resemble each other and are considered to undergo convergent evolution :explode:
only phenotypes converge not genotypes :<3:
if tow distinct, unrelated species occupy the same area, Natural selection may favor same phenotype in each :check:
example are desert plants (cacti) in Americas and Africa
Rates of Evolution
very few mutations produce a new phenotype superior enough to out compete all other members in a population
extreme, some seedless plants can go for millions of years without diverging where others can diversify rapidly creating a new species every 500k years
does not happen very rapidly :timer_clock:
hard to identify presence of particular alleles in population unless it produces noticeable effect on phenotype :check:
new allele only creates a new adaptive structure if it fits into the highly integrated mechanisms without disruptive effects :red_flag:
probability can decrease as system becomes more intricate
causes most studies to be concerned about physical developments
changes that cause loss of structure are due to complexity of the system as well :check:
if disruptive mutations outnumber constructive mutations, loss can occur rapidly :red_flag:
if feature is selectively disadvantageous, many mutations that disrupts its development become selectively advantageous :checkered_flag:
Evolution and the Origin of Life
Chemicals produced chemosynthetically
rocks brought back from the moon contained amino acids :new_moon:
meteorites uncontaminated by atmosphere or soil have contains alcohols, amino acids, sugars, nitrogenous bases :check:
first test to test hypothesis was done by graduate student S. Miller who stimulated lightning is a closed environment
after a week, chemicals in the water included amino acids :!!:
since then this was the basis of every other similar experiment with different factors added depending on the test.
was left on for a week after reporting that chemicals were made and dropped in water and cycle was repeated :recycle:
all small molecules essential for life was produced in these experiments :star:
Formation of Polymers
obvious method was formation of seaside pool at high tide that evaporate when tide leaves :ocean:
when high tide returns, polymers are washed back into ocean and accumulate
monomers could have been accumulated in ponds and pools when frozen :snowman:
may have produced a distinct polymer than those that were heated
pools would have heated warm enough to cause polymerization reactions to occur :check:
monomers present in early ocean had to polymerize if life were to arise but required high concentrations of monomers :check:
over time would transform from dilute soup to concentrated one but was not necessary
numerous mechanisms would have :check: produced pools of highly concentrated reactants
Absorption by clay particles could have high concentrations of monomers :star:
contains ions of iron, magnesium, calcium, phosphate, and other charged groups that are present at activation sites of enzymes :check:
might have both concentrated monomers and acted as the first primitive catalyst
structure is crystalline and organic molecules will bond to the particular orientations, not at random
Conditions on Earth Before the Origin of Life :check:
Energy Sources :zap:
Heat was another source of energy to power reactions. :fire:
one source of heat was coalescence of gas and dust to form Earth
another source was radioactive decay :radioactive_sign:
electricity due to the water in the atmosphere was another source of energy :potable_water:
in the form of lightning in storms :tornado:
when volcanoes erupt they also produce lightning :volcano:
powerful reducing agents, intense UV and gamma radiation broke down ammonia making H+ and N and CH4. :black_flag:
would be converted to carbon monoxide and carbon dioxide increasing complexity of atmosphere
Time available for the Origin of Life
the time of chemosythesis had no time limit due to lack of free molecular oxygen :check:
no agent was present to cause breakdown and decomposition of chemicals being created
if O2 had been present, chemicals either not form or oxidized after formation, without O2 was allowed to accumulate :star:
Ocean at the time was considered dilute soup/primordial soup containing water. salt, and numerous organic compounds that became complex with time
Chemicals Present in the atmosphere :checkered_flag:
would have provided gases such as hydrogen sulfide, ammonia, methane, and water found in volcanic gases and meteorites
early second atmosphere was a reducing atmosphere due to lack of molecular oxygen and presence of powerful reducing agents :<3:
hydrogen majority in atmosphere caused it to be lost in space, created 2nd atmosphere from gases of rock matrix :star:
Aggregation and Organization
fatty, hydrophobic material would have accumulated, fatty acids on the outermost layer, with proteins that were
hydrophobic, would be contained in the interior but some proteins had hydrophobic exterior and hydrophilic interior
aggregation of certian types of proteins would have resulted in large regions of hydrophilic sites :check:
first aggregations would have formed at random controlled only by relative solubility :star:
if some had enzymic activities, would have been a simple metabolism :red_flag:
these aggregates would have been heterotrophs completely
next step for chemical life would be aggregation of chemical components into masses that had some organization and metabolism :star:
these early aggregates were not considered alive as they stored no genetic information :red_cross:
these dead aggregate would have contributed to composition of ocean
some however could have had very active enzymes producing complex enzymes :check:
without this natural selection cannot occur
some could have degraded said products and establish equilibrium between destruction and formation :green_cross:
at some point an aggregate formed that had a heritable information molecule able to direct synthesis of products :black_flag:
may help aggregate to grow and even replicate the information molecule
the presence of the information molecule allowed mutations, selective advantages, and natural selection
would have produced products that would help plant to survive longer :zap:
most seriously considered hypothesis about origin of life on Earth is that of chemosynthesis :star:
chemosynthesis attempts to model origin of life using only chemical and physical properties
four conditions for chemosynthesis, primitive Earth had to :!:
appropriate energy sources
a great deal of time
have the right inorganic chemicals
absence of oxygen in its destructive molecular O2 form
The Presence of Life
chemosynthesis theory delineates no absolute demarcation between living and non-living things
chemistry of living things is very complex yet they are identical to nonliving things in terms of physics
chemosynthesis theory postulates :check: a long series of slow gradual transitions from inorganic compounds to bacteria
in living world we deal with continuum not two different alternatives making it more important to understand processes in their complexity
Oxygen
rusting period was critical for life as it limited the content of molecular O2 in atmosphere :warning:
free oxygen is essential to live but is dangerous
years of oxidizing iron was considered an environmental hazard millions of years ago but was not universally lethal
many plants an animals have adapted to control molecular O2 so that it does not harm us at random
oxygen was then turned form dangerous pollutant to valuable resource due to evolution of mitochondria and cytochrome
as water became raw material for photosynthesis, free molecular O2 was released as waste product
after all iron was oxidized, oxygen then started to accumulate in the atmosphere creating the early secondary atmosphere :recycle:
present day atmosphere is considered a oxidizing atmosphere :cloud:
occured around 2.8 billion years ago, because of combination of iron and O2 created rust found in sedimentary rock :explode:
build up of O2 allowed creation of O3, ozone :dark_sunglasses:
removed UV light as an energy source :no_entry:
lack of UV light made Earth safer to live in, due to UV destruction of nucleic acids :red_cross:
ozone protects Earth form UV light and solar radiation :+1:
without ozone, life would be stuck under the ocean, with ozone, life was able to adapt to life on land :beach_with_umbrella:
evolution of chlorophyll a and photosynthesis that liberated O2 had 2 profound effects :check:
allowed the world to rust :truck:
created conditions that selected for the evolution of aerobic respiration
until this time, photosynthesis involved bacterial pigment bacteriochlorophyll that liberated sulfur from hydrogen sulfide :explode:
Early metabolism
energy metabolism was also very important
would later absorb ATP through fermentation in a few million years
electron pumping system would be added and photosynthesis would become more complex with time
glycolysis must have evolved from these early stages as it is present in all organisms :check:
mitochondrias would not have evolved with the presence of molecular O2 in the early stages of life :warning:
natural selection would favor any genetic system to adapt to involve more steps in the metabolic pathways :star:
would soon become water and carbon dioxide in modern plants
aggregates would have been completely heterotrophs absorbing materials from the ocean and modifying some molecules :check:
ability to adapt one molecule to be used to for multiple functions was advantageous
selective advantage was strong with more complex metabolic pathways
would cause a shortage of particular molecules
