Transcript Process 1 - Blended Biology

Option D
Rachel M.
Michal
Enkhjin
Describe four processes needed for
the spontaneous origin of life on earth.
• Process 1: synthesis of simple organic molecules
• Process 2: assembly of simple organic molecules
into polymers
• Process 3: formation of polymers that can selfreplicate
• Process 4: the packaging of these molecules into
membranes with an internal chemistry different
from their surroundings, including polymers that
held the genetic information.
Outline the experiments of Miller and
Urey
• simulate reducing atmosphere
– Miller/Urey: water vapor, hydrogen, methane,
ammonia
• simulate high energy source
– Miller/Urey: electric spark simulates lightning
• Products
– Miller/Urey: mixture of amino acids
State that comets may have delivered
organic compounds to Earth
• Comets contain a variety of organic
compounds. Heavy bombardment about
4,000 million years ago may have delivered
both organic compounds and water to the
early Earth.
Discuss possible locations where conditions would
have allowed the synthesis of organic compounds
Examples should include communities around deep-sea
hydrothermal vents, volcanoes and extraterrestrial locations.
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Deep sea vents: ammonia and methane are present, and were
not present elsewhere in the early atmosphere. There are many
organisms currently living around deep sea vents suggesting this is a
possible explanation.
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Volcanoes: volcanic eruptions involve the release of methane,
ammonia, and hydrogen gases as well as water vapor. This, when
combined with lightning, creates a real-life version of the MillerUrey experiment.
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Extraterrestrial locations: Comets contain a variety of organic
compounds. Heavy bombardment may have delivered both organic
compounds and water to the early Earth.
Outline two properties of RNA that would have
allowed it to play a role in the origin of life
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Scientists believe that RNA is most likely to have been the first genetic material on
Earth. DNA replication requires enzymes and enzymes did not exist on prebiotic
Earth. Under certain conditions RNA can replicate itself without the use of
enzymes which makes it the more likely candidate for the first genetic material.
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Research has shown that RNA can carry out a number of enzyme-like catalytic
functions. They can also make complementary copies of short pieces of RNA as
long as it has the nucleotides needed to build the RNA.
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They believe that small molecules of RNA which had the ability to carry genetic
information also had the ability to replicate and store information about the celllike spheres (protobionts) they were carried in.
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This RNA found in protobionts would have carried very limited genetic
information and the most successful protobionts would flourish and increase in
numbers (natural selection).
State that living cells may have been preceded by
protobionts, with an internal chemical environment different
from their surroundings
• When clay dries amino acids can spontaneously from polypeptides
and in the right conditions a protenoid microsphere can be formed
from these chains. These tiny bubble-like structures could surround
other polymers and allow condition inside the microsphere to
remain different from the external environment.
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There could also be another sphere known as a coacervte; a lipid
sphere that forms in water due to the hydrophobic properties of
lipids. These microspheres could also keep a different internal
chemical environment along with eh capacity to be selectively
permeable.
• These structures are both known as protobionts and they are
considered an important step in the formation of cells.
Outline the contribution of prokaryotes to the
creation of an oxygen-rich atmosphere
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Bacteria, specifically anaerobic bacteria are believed to be the first
forms of life on Earth. They consumed organic materials and
reproduced to such numbers that competition was high and food
was scarce.
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It is unclear how it happened but some bacteria evolved to become
photosynthetic. When this happened they began releasing a waste
product into the air called oxygen. Some of the oxygen killed off
the high population of bacteria and the ones who survived were
living deep in the mud or other areas protected from the oxygen in
the atmosphere.
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The ability to make its own food led these prokaryotes to
reproduce and increase in significant numbers further increasing
the oxygen in our atmosphere.
Discuss the endosymbiotic theory for
the origin of eukaryotes
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Prokaryotes or bacteria were the first forms of life on Earth and the only form from 3.8 billion to
about 2 billion years ago. Scientists know this because that is when fossils started showing cells
that contain a nucleus, unlike the prokaryotic cells.
The theory of endosymbiosis is a widely accepted theory that attempts to explain how prokaryotes
evolved into eukaryotes; cells with a nucleus and membrane bound organelles. The theory states
that large organelles inside eukaryotic cells such as the mitochondria and chloroplasts were once
independent organisms that were taken in by a bigger cell and kept alive to perform important
functions.
It is believed that some cells lacked an enzyme needed to digest the prokaryote so instead the
engulfed cell stayed alive inside the host cell and increased the cell’s ability to produce energy.
By natural selection the cells with the ability to photosynthesize or metabolize nutrients efficiently
would be most likely to survive and flourish.
This theory explains how mitochondria and chloroplast became part of eukaryotic cells and it is
supported by characteristics of these two organelles which make them different from the
others. First of all they have their own DNA; a naked loop similar to that of prokaryotes. Secondly,
they have their own double membrane. Thirdly, they are able to replicate themselves when more
are needed and last they have the ability to perform protein synthesis using ribosomes.
Although there are many questions answered by this theory several still remain. There is no
guarantee that an engulfed cell would be copied and passed onto offspring. Also, when you
remove a mitochondrion or chloroplast from a cell they cannot survive on their own.
Define allele frequency and gene pool
• Allele frequency: proportion or percent of a
specific variation of a gene in a population.
• Gene pool: all of the genetic information
present in the reproducing members of a
population.
State evolution involves a change in allele
frequency in a population’s gene pool over a
number of generations
• Evolution results in changes to some alleles
after many generations of natural selection.
Alleles that have proven to be advantageous
become more frequent while those that as
disadvantageous are not assed on to the next
generation. Immigration and emigration can
also have an impact on allele frequency within
a population’s gene pool.
Discuss the definition of the term
species
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The morphological definition of the term species states that it is a type of
living organism with fixed characteristics that distinguish it from other species.
This definition is very helpful in identifying organisms that have similar
physiological and morphological characteristics, the ability to interbreed to
produce fertile offspring, genetically distinct from other species, and have a
common phylogeny. The biological definition of a species is a group of actually
or potentially interbreeding populations with a common gene pool, which are
reproductively isolated from other such groups. There are some complications
or challenges to the biological definition of a species and they include the
following. Some members of separate but similar species reproduce
successfully and produce an offspring that is of neither species. The zonkey at
the zoo in Aylesford is an example of a hybrid. The offspring however is
infertile because the chromosome numbers are not the same in the parents.
Another example is a liger as seen below. It is a hybrid of a male lion and
female tiger. The hybrid is considerably larger than either parent.
Describe three examples of barriers between gene
pools.
• Geographical isolation: physical barriers that prevent males
and females from seeing each other. (e.g: mountains and
rivers).
• Temporal isolation: incompatible time frames for mature
gametes to come in contact with one another. (e.g: if
female part of flower reaches maturity before the pollen is
released or vice versa it will make reproduction difficult)
• Behavioral isolation: the habits and lifestyles of one
population do not match that of another population. (e.g:
many species of birds rely on courtship display to initiate
sexual reproduction.)
Explain how polypliody can contribute
to speciation
• Speciation is the process of a population that
is evolving which changes so significantly that
producing an offspring with a member of the
original population is impossible.
• Polypliody refers to the situation in which a
cell contains 2 or more sets of chromosomes.
You have previously
Outline the process of adaptive
radiation
Adaptive radiation is when a species divides, and then evolves in
different ways depending on their environment to fill their ecological
niche. This evolution occurs because some species are better suited to
inhabit that environment, so they have a better chance of surviving
longer and creating offspring.
On the Galapagos islands, for example, finches have evolved into about
13 different species which all stem from the same ancestor species.
These species are varied from the ancestor species in order to fill the
niches of the different islands.
Compare convergent and divergent
evolution
• Convergent evolution is when different species
become more similar over time, sharing
analogous traits due to the environment’s niche.
• Divergent evolution is when the same species
evolves in such a way that differences appear in
individuals in a species, and groups become less
and less similar over time. This is usually due to a
group of organisms separating to different
environments.
Discuss ideas on the pace of evolution, including
gradualism and punctuated equilibrium
• Gradualism is the slow change of a species from
one form to another. This could happen if an
environment is not especially extreme, so
changes can happen more slowly and species
don’t need to evolve rapidly in order to stay alive
• Punctuated equilibrium implies long periods
without appreciable change, and then short
periods of rapid evolution. This would take place
if an environment changed rapidly, causing a
need for a species to evolve if they want to have
any hope of survival.
Describe one example of transient
polymorphism
• Transient polymorphism is when the frequency of
a phenotype changes in an area over time.
• Example – During industrialization in England,
dark colored peppered moths gradually became
more dominant in England than lighter-colored
peppered moths, due to the environment. This is
because trees became darker and darker as
industrialization polluted the area, so darker
moths blended in well and avoided being pecked
by birds or preyed upon.
Describe sickle-cell anemia as an
example of balanced polymorphism
• When an individual has homologous recessive
trait for sickle cells, they will have sickle celled
anemia, because their red blood cells will be
sickle shaped. However, when an individual
only has one allele for the trait (making them
heterozygous), they become resistant to
malaria. For this reason, the gene for sickle
cell has not died out. So, the frequency of the
gene remains balanced and constant-ish.
Outline the method for dating rocks and fossils
using radioscopes with reference to 14C and 40K.
• Fossils contain elements called isotopes from the
living matter that used to exist. If isotopes are
unstable, they will decompose over time. Each
radioactive isotope has a fixed half life, and using
the relative abundance of reactants and decayed
products in a substance, biologists can estimate
the age of fossils. 14C (Carbon 14) has a half life
of 5000 years, so it can be helpful in identifying
the age of fossils younger than 100,000 years old.
Potassium-40 (40 K) has a half life of 1.3 billion
years, so it’s more useful in identifying much
older fossils.
Define half-life
• An element’s half life is the amount of time it
would take for half of a radioactive element to
decay.
Deduce the approximate age of materials based
on a simple decay curve for a radioisotope
• Count how many times the abundance of
radioactive isotope has halved (when it’s ½
the original concentration, then ¼, then 1/8,
then 1/16, etc…). Next, evaluate how long it
took for the isotope to halve. Multiply the
number of years in one half-life by the
number of halves that have taken place.
Describe the major anatomical features
that define humans as primates
• Vision: eyes are close together on the front of the face, allows for
over-lapping fields of vision and good depth perception (3D). Color
vision.
• Parental care: humans (and primates) have a longer gestation
period that other mammals and single births are the norm. Long
nurturing period for offspring.
• Dexterous hands with opposable thumbs. Nails on digits. Tactile
pads at the end of digits.
• Collarbone: allows for a flexible shoulder joint, which allows for
movement in 3 dimensions.
• Brain size: brain is larger and more developed/complex than most
other mammals.
• Teeth are arranged so primates can have an omnivorous diet.
Outline trends illustrated by the fossils of Ardipithecus ramidus,
Australopithecus including A. afarensis and A africanus, and Homo including
H. habilis, H. erectus, H. neanderthalensis, and H. sapiens
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Trend: migration out of Africa
Trend: increased adaption to bipedalism (pelvis, fully extendable knees, stronger
legs/weaker arms, platform-like foot without opposable toes)
Trend: decreasing relative size of face, jaw, teeth, especially canines; increasing
relative size of brain case, forehead.
A. afarensis: 3-3.9 million years, ape-like face.
A. africanus: 2.3-3 millions years. Flatter face, larger molars for plant based diet.
A. robustus: 1-2.2 million years. Very large bones, molars and skull.
H. habilis: 1.6-2.4 million years. Smaller teeth and jaw for a meatier diet. First to
use tools. Sized like humans.
H. erectus: .4-1.8 million years. More complex tools – thus meat is a bigger part of
diet. Teeth changed.
H. neanderthalensis: .5 million years. Larger brains and bones, large teeth and jaw,
shorter limbs for the cold.
H. sapiens: .1 million years. Large brain, flat face, reduced teeth, reduced
robustness, chin.
State that, at various stages in hominid
evolution, sever species may have coexisted.
• Yes, several species may have existed at once
during hominid evolution. For example, habilis
and erectus most likely existed at the same
time, as well as erectus and neanderthalensis,
and neanderthalensis and sapien.
Discuss the incompleteness of the fossil record and
the resulting uncertainties about human evolution
• In order to tell the age of fossils it is helpful for all the
bones in a body to have been distributed and
preserved in one place. Because many hominids were
preyed upon, fossils are spread out. An organism also
needs to have hard parts and be buried in an anaerobic
environment very quickly, which wasn’t always the
case. There are a lot of missing links in between species
and it is hard to say with certainty when certain species
officially died out or began.
• It cannot be ensured that the hypothesis for hominid
evolution is complete or accurate.
Discuss the correlation between the change in
diet and increase in brain size during hominid
evolution
• Larger brains require more energy to operate. A
change in diet from mostly veggies to including
more meat would support and increase in brain
size because meat is generally a little more caloric
and fatty, and would support the usage of brain
energy. Protein increase also enables brain
growth.
• Also, hunting and killing prey on savannas is more
difficult than gathering plant foods, so natural
selection might have favored larger brains with
greater intelligence.
Distinguish between genetic and
cultural evolution
• Cultural evolution is a difference in the behaviors and
mannerisms of a species, for example a change in
traditions or tools used, types of shelters created,
things eaten, etc.
• Genetic evolution is a change in the genetic make-up of
a species.
• Genetic evolution (increase in brain capacity) hasn’t
really changed much in homo sapiens. Cultural
evolution, however, constantly changes. A lot of our
evolution as a society draws on our experiences as a
species, and that kind of past knowledge, not
necessarily advanced intelligence.
Discuss the relative importance of genetic and
cultural evolution in the recent evolution of humans
Evolution of the brain allowed cultural evolution to take off. Since
then cultural evolution has been able to change humans far more
quickly than genetic evolution has. Human behavior and life has
changed greatly without much genetic evolution at all. We are
now able to change our environment instead of changing to suit
our environment
Explain how the Hardy-Weinberg equation is derived
p squared + 2pq +q squared = 1
• p represents the frequency of the dominant
allele and q the frequency of the recessive
allele
• When gametes combine their alleles to form
zygotes, the probability of AA (A being the
dominant allele) is p squared. The probability
of aa is q squared. There are two ways in
which an Aa genotype can arise, depending on
which parent contributes the dominant allele.
Calculate allele, genotype and phenotype frequencies for two
alleles of a gene, using the Hardy-Weinberg equation
• 1600 people were tested in a survey. 461 were non-tasters a frequency of 0.288.
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Their genotype was homozygous recessive (tt).
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If q = frequency of t allele, q squared = .288 so q = .537
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If p = frequency of T allele, p = (1 - q) = .463
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The frequency of homozygous dominants (TT) and
heterozygotes (Tt) can be calculated.
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p squared = frequency of homozygous dominants
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p squared = (.463)(.463) = .214
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2pq = frequency of heterozygotes
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2pq = 2 (.463)(.537) = .497
State the assumption made when the Hardy-Weinberg equation is
used
• A population is large, with random mating and
constant allele frequency over time. This
implies no allele-specific mortality, no
mutation, no emigration and no immigration.
Outline the value of classifying organisms
• classification arranges organisms into groups
• classification allows identification of species / organisms
• classification allows prediction of related taxa / based on
common characteristics
• classification reveals evolutionary links / shared derived
characteristics / inherited from common ancestors
• classification allows effective communication / all scientists
use same terminology
• classification avoids problem of convergence / ignores
analogies
• classification emphasizes homologous structures / traits
derived from common ancestry
Explain the biochemical evidence provided by the universality of DNA
and protein structures for the common ancestry of living organisms
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DNA/genetic code is universal;
same four bases adenine, cytosine, guanine and thymine; To award the mark full
names of all four are required.
always pairing of A T and G C;
same structure of double helix of complementary strands;
use the same 20 amino acids in their proteins;
all left-handed;
same/similar enzymes in processes of replication/transcription/translation;
small differences in DNA/proteins show closer relationships;
e.g. hemoglobin/cytochrome C/gene structures show relationships among
organisms;
humans have the same biochemistry as all organisms so part of same evolution/
common ancestry;
mitochondrial DNA used to determine maternal lines / y chromosome used to
determine paternal lines;
endosymbiotic theory/mitochondria/chloroplast structures indicate common lines
of evolution;
Explain how variations in specific molecules can indicate
phylogeny
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differences between molecules can be used to deduce phylogeny
phylogeny is the evolutionary history of a (taxonomic) group
mutation rates in DNA occur with predictable rates
compare nucleotide sequences (of DNA) between taxa
compare amino acid sequences (of proteins) between taxa
differences can be used as a molecular clock
to develop phylogeny
to determine time since common ancestry
variation can be due to mutations;
mutations are chance events so caution must be taken when
interpreting these
Discuss how biochemical variations can be used as an
evolutionary clock
• differences in nucleotide base sequences / DNA /
amino acid sequences / proteins
• accumulate gradually over time
• differences accumulate at (roughly) predictable rates
• therefore the number of differences can be used as a
clock
• to measure the time since two divergent groups shared
a common ancestor
• example; e.g. amino acid sequences in globin genes
Define clode and cladistics
• Clade: a group of organisms that evolved from
a common ancestor
• Cladistics: a method of classification of living
organisms based on the construction and
analysis of cladograms
• Nodes: branch points indicating the evolution
of shared derived characteristics
Distinguish, with examples, between analogous and homologous
characterisitcs
Analogous Characteristics:
•analogous characteristics are structures with a
common function
•but a different evolutionary origin
•example: dolphin fins and shark fins
Homologous Characteristics
•homologous characteristics are structures that
have a common evolutionary origin
•even if they have different functions
•example: dolphin forelimbs and human arms
Outline the methods used to construct cladograms and the
conclusions that can be drawn from them
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The first step involves the construction of a list of all organisms that will be
included in the cladogram.
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The next step involves compiling a list of characteristics possessed by these
organisms. This list would normally involve morphological characteristics but a
cladogram can be constructed based on biochemical data also.
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Now you would need to look at the one trait that is common to all organisms
and this would be the primitive characteristic (i.e., eukaryotic, multicellular,
vertebrae).
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Ø The next step is to construct a table showing all of the derived characteristics
on the top row and the names of the organism in column one.
Discuss the relationship between cladograms and the
classification of living organisms
• cladograms (often) confirm existing classifications
• since both are based on phylogeny
• cladograms are (sometimes) different than traditional
classifications
• because nodes can be placed at any point / arbitrary
• cladograms (sometimes) radically alter existing
classifications
• example: birds grouped with dinosaurs
• strength of cladistics is that the comparisons are objective /
rely on molecular homologies
• weakness of cladistics is that molecular differences are
based on probabilities