Maintaining A Balance - HSC Biology 2012 Notes
Peter Richardson
EVOLUTION
Evolution = really means CHANGE
Evolution is not intelligent, it simply selects survivors.
~ The result of eons of evolution is an enormous diversity, superficially very
different but fundamentally related through their shared ancestry.
Changing Conditions
Any change in an environment will result in Natural Selection selecting
different characteristics.
Variation is
Variation exists within the population due to slight
differences in genetic code (mutations). Individuals with the favorable variations
are more likely to survive and reproduce, thereby passing on favorable genes to
future populations
Physical conditions
❖ The earth is an ever-changing place. It has been changing since itʼs formation about
4.6 billion years ago. Continents continue to move and become drier, colder, wetter or
warmer; seas, coastlines, forests and deserts come and go; and water, wind,
earthquakes and volcanoes shape the land. Fossils show Australia used to be covered
in luscious forest with a much wetter climate.
❖ Changes in the environment force species to either die out, or survive and diversify
A good example - the Peppered Moth
light-patterned lichens
During Industrial Revolution
trees are blackened.
Chemical conditions
❖ Chemical changes in the environment impact on the evolution of organisms by
acting as a selection pressure that decides which organisms are the ʻfittestʼ.
❖ Example; When DDT an insecticide was used against diseased mosquitos or crop
eating pests, the insects eventually developed an genetic resistance. The ones with
this resistance survived, passed on their genes and now the population is mainly
resistant. Their gene pool had changed.
Competition for resources
❖ If a new species is introduced into an area then the competition may lead to different
species using different resources. Or consequently, the species could die. If populations
that live in the same area could specialise on slightly different resources, they would avoid
direct competition.
Maintaining A Balance - HSC Biology 2012 Notes
Peter Richardson
Evidence For Evolution
Paleontology
Fossils are preserved traces of life.
• is the study of fossils. The fossil record provides a timeline of evolution of life;
engraved in the order in which the fossils appear in rock layers. Paleontologists can trace
and date evolutionary changes in organisms.
• The record shows a gradual change in life forms over millions of years.
• Transitional Forms; Transitional forms are examples of organisms that indicate
development from one group of organisms to another. They help us to understand
how an evolutionary change may have came about.
Archaeopteryx
Had teeth and a reptilian-like skeleton. However it also had
feathers and wings! This provides evidence of an evolutionary
pathway from dinosaurs to birds.
Biogeography
• Is the study of the distribution of living things. When Charles Darwin first travelled
around the world, it was the distribution of different types of life in different places that first
gave him the idea for evolution.
• These distribution patterns provide evidence that species have originated from common
ancestors and, when isolated, had adapted overtime to the different conditions.
Australia & Asiaʼs Unique Flora & Fauna
The explanation for the endemic (Unique) flora and fauna in
Australia is based on biogeography. This phenomenon was first
descried by Alfred Wallace, who suggested a line (now called
Wallaceʼs Line) to separate the distribution of these organisms.
Comparative Embryology
• The embryos of many different organisms
(particularly terrestrial vertebrates) are
remarkably similar.
• Evolution explains this as the results of all these
animals evolving from a common ancestor which
had an embryo like this
• They may have a gill pouch as some stage
(humans) which suggest an evolution from a
common aquatic ancestor.
Maintaining A Balance - HSC Biology 2012 Notes
Peter Richardson
Comparative Anatomy - Homologous structures
• When body structures of different organisms are compared, it is often obvious that
they sometimes share common features, even though the body parts might be used
in very different ways and in very different lifestyles.
Pentadactyl Limb (ʻPentaʼ = 5, ʻdactylʼ = Fingers)
- A structure of bones found in many vertebrates.
• Further evidence of an structure inherited by a common
ancestor.
• one forearm bone, to dual lower arm group, and wrist bones
to digits
Biochemistry
• Cells from the most simplest to the most complex of organisms
share certain fundamental properties, which can be seen at the
biochemical level.
- All cells have a nucleus (eukaryotes) or a nucleoid (bacteria or
archaea [also called prokaryotes]) that contain the Genome
(where the haploid set of of genes, composed of DNA are
stored and replicated)
- The same Plasma Membrane
• Similarities in the base-pairing of DNA strands (DNA hybridisation)
has been analysed to show evolutionary links.
• The analysis of amino-acid sequences in proteins, provides
evidence for evolution in general.
New technologies, particularly in the field of biochemistry, have increased our knowledge about the
relationships between species. E.g. DNA Hybridisation; has found that we are more closely related to
chimpanzees than previously thought.
Divergent Evolution (also known as adaptive radiation)
When closely related species (common ancestor) experience quite different
environments (due to isolation) and as a result, adopt vastly different characteristics.
The species, over time, will differ so much that they become a new species.
Darwin's Finches
Galapagos Islandʼs far apart: the finches from each
island population became distinct.In each pop. an
individual happened to acquire a random mutation of
a beak more suitable to food sources of that locality.
Therefore giving that individual the competitive edge,
and allowing the individual to pass on characteristics.
Convergent Evolution
If totally different organisms live in the same kind of environment, over many
generations they will evolve many of the same features due to that environment.
The Shark (fish) & The Seal (mammal)
Both live in the ocean, & have the
same streamline shape, and powerful tail yet are
completely unrelated.
Maintaining A Balance - HSC Biology 2012 Notes
Peter Richardson
Societies Acceptance of the Evolutionary Theory
Charles Darwin
•
•
•
Christianity was very dominant force during his time.
Evolution was running against the accepted ideas of
Creationism.
He knew what a huge impact his theory would have, and
chose to withhold publishing it for 25 years. Until during
the Industrial Revolution when the power of the church
was tested. - Charles Darwin's results still caused great
debate.
Alfred Wallace
Model of Natural Selection
Gregor Mendel
In Charles Darwinʼs life time no one could explain where variation in a species came
from, or how characteristics where transferred from one generation to the next. The
founder of the modern science of genetics was Austrian monk Gregor Mendel.
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Mendelʼs Experiment
Mendel chose garden peas because they were easy to grow, produced new
generations quickly and had easily distinguishable characteristics.
Before he began, it is important to note, he selectively bred each plant for 2 years to produce
only Pure-breeding Offspring. This meant that if they where self-pollinated they would always
produce identical offspring.
F1
CROSS POLLINATED
F2
(first generation)
Side note : Filial : Denoting the generation or generations after the parental generation
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Maintaining A Balance - HSC Biology 2012 Notes
Peter Richardson
Mendelʼs Conclusions
Inheritance is not a ʻblending of characteristicsʼ as was commonly believed.
He deduced that each characteristic was controlled by ʻfactorsʻ (we call them genes)
An individual inherits only one factor (gene) from both parents
A trait may not be visible (its phenotype) but will still be passed on genetically. (recessive)
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Experimental techniques that led to his success
-
He didnʼt just use 1 or 2 plants - he used large numbers of plants. He got the same result
from pod shapes, flower colours & so on.
-
He chose easily-identifiable characteristics which occurred in just two forms. E.g. tall stem /
short stem.
-
He began with ʻpure-breedingʼ parent plants.
-
He strictly controlled fertilization (hand pollination) to maintain accuracy.
F1
F2
Punnett squares are
not 100% precise,
they are statistical
measures only
~ there is a random
chance.
Ratio of phenotypes 3:1
3 Dominant to 1 Recessive
Monohybrid Cross (mono meaning 1) A genetic cross made to examine the
distribution of one specific set of alleles in the resulting offspring. Mendel
only observed one characteristic at a time. Example: tall peas x short peas or
TT x tt
Dihybrid cross : 2 alleles e.g TTRr
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Why his results were not recognised
- He was not a recognised scientist / he did not have a great access to the scientific community.
- His work was written only in German / all the ʻimportantʼ science of the time was appearing in
english or french
- His work was radical. Scientists of Mendelʼs time had little knowledge about cells and nothing was
known about chromosomes and genes. Improvements in microscopes and technology have since
been able to examine cell nucleusʼ and DNA.
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Hybridisation
The aim of hybridisation, is to take desirable characteristics from two animals in a species and
combine them to form a hybrid organism.
To help combat the effects of
drought and ticks
as well as producing better meat
Brahman
Hereford
Bradford
Maintaining A Balance - HSC Biology 2012 Notes
Peter Richardson
23 Chromosome PAIRS
23 from Father
23 from Mother
every cell in
the body has
this set, except
gametes (germ cells)
A pair of chromosomes are
called homologous because
they essentially code for the
same thing.
Gene
a section of DNA on a chromosome that codes for a particular
characteristic
Allele
Each individual chromosome has a pair of genes for a certain
characteristic. The members of this gene pair are called alleles.
Tt
Dominant Allele Recessive Allele
22 chromosome pairs, the 23 pair are Sex Chromosomes
Female - XX
Male - XY
Homozygous The Same TT, tt
Heterozygous Different Tt, tT
Eukaryote nucleus
Haploid : HALF the amount of
chromosomes
Diploid : FULL amount of
chromosomes
Prokaryote no nucleus
homologous chromosomes ;
(a pair) They code for the same
genes, but may have different
alleles.
Sutton and Boveri
Together, Sutton and Boveri are considered to be the founders of the Sutton-Boveri
Chromosome Theory. Suggesting that Mendel’s ‘factors’ are carried on
chromosomes, their work attempted to establish a parallel between Mendel’s laws
and chromosome behavior.
Sutton:
Studying grasshopper chromosomes during meiosis, he found that the behavior of
chromosomes during cell division and fertilisation matched the behavior of factors
(genes) as described by Mendel. He showed that chromosomes were distinct entities,
even though they duplicate and divide they remain as a distinct structure.
Boveri:
Studying sea urchins Boveri showed that a complete set of chromosomes was vitally
necessary for the normal development of an organism.
Maintaining A Balance - HSC Biology 2012 Notes
Peter Richardson
DNA
Side note: Chromosomes consist of 40% DNA and 60% Protein.
(Deoxyribonucleic Acid)
- DNA is a extremely long molecule. To be able to fit into a cell nucleus, the
DNA strand must be tightly coiled around special structural proteins called
histones.
NUCLEOTIDE
A - T
Adenine
Thymine
C - G
Cytosine
Guanine
Also notice that, the
other nucleotide strand
is flipped ( it goes in the
opposite direction )
Mitosis
• All our Somatic Cells (those occurring within the body) except gametes use mitosis for cell division
(for growth or repair)
• In mitosis one division occurs, forming an exact copy of the parent cell chromosomes
IDENTICAL TO
PARENT CELL
Result in TWO
DIPLOID cells
SINGLE DIVISION
OCCURS
Meiosis
• Sexual Reproduction
- Gamete Cells (Sex cells)
NOT GENETICALLY IDENTICAL
TO PARENT CELL
Result in FOUR
HAPLOID cells
Meiotic Stages
Maintaining A Balance - HSC Biology 2012 Notes
Peter Richardson
✴ Interphase
- Prior to meiosis or mitosis, DNA replication occurs. - Chromosomes become condensed, &
can be viewed under the microscope. (previously tangled, canʼt see chromosome form)
- Each strand generates an identical copy of itself called a Chromatid. The new chromosome
connects to the old one using a centromere. (Centrioles duplicate in this phase also)
✴ Prophase
- Homologous chromosomes pair up, and crossing over occurs.
- Nucleus envelope begins to break apart
✴ Metaphase
- Chromosomes are aligned by the spindle fibers of the Centrioles
✴ Anaphase
- Chromosomes are drawn to the opposite side of the cell
✴Telophase
- Nucleus re-forms and the cellʼs cytoplasm is divided by Cytokinesis
In the first meiotic division, the homologous
chromosomes separate, but the double strands of
the chromosomes are still joined.
In the second division, the chromatids of the
chromosomes separate and form 4 gametes
altogether.
Centriole
Spindle Fibers
Variation comes from MEIOSIS and Sexual
Reproduction!
I.
Centromere
During the process of meiosis, one chromosome from each of the 23 diploid pairs
must be contributed to form the haploid gamete. Which chromosome is
23
selected is completely random.
This gives 2 possibilities
When a male and a female sexually reproduce, this
combines the two gametes to form a zygote.
46
This gives 2 possibilities
II.
The crossing over that occurs in the prophase of meiosis provides even an almost limitless
scope for the variation that can occur.
Sex-linked Genes & Thomas Morganʼs Fruit Flies
- Genes that are carried on the sex chromosomes, either on the X or Y, are called
sex-linked genes.
- Morgan realised that the inheritance of some characteristics could not be
explained with simple Mendelian crosses. He found that the way this
characteristic was being inherited depended on the sex of the fly... male and
females where inheriting eye colour differently!
- Morgan produced hundreds of flies in the experiment, like Mendel, his results
where statistically significant.
fig.1
Drosophila
Dominant eye
colour red
Maintaining A Balance - HSC Biology 2012 Notes
His hypothesis was that Y did not carry the gene only X in this case
Peter Richardson
There are a number of genes in humans that are sex linked.
(e.g. Haemophilia or Colour Blindness) Both conditions are inherited as recessive genes on the X
chromosome. They occur much more often in males than in females.
E.g. Roan Cow
Co-Dominance
- In simple dominance cases, if a gene is homozygous dominant, the
phenotype is obviously that of the dominant allele (HH or RR). If it was
homozygous recessive it is obviously that of the recessive allele. (hh
or rr)
- If the gene is heterozygous, than the dominant allele would be the
phenotype of the organism, as the dominant allele would of course
take precedence over the recessive. (Hr)
- HOWEVER, if it was a case of co-dominance, heterozygous
organisms would have both phenotypes expressed at the same time.
No allele is dominant or recessive. (HR)
- The result is not in fitting with Mendelʼs simple 3:1 ratios.
~ It results in a ratio of 1:2:1
The Effect of the Environment on Phenotype
1:2:1
GENES + ENVIRONMENT = PHENOTYPE
- Itʼs not just an organismʼs genes that produce its phenotype; The environment has an
effect as well!
- The environment can control to what extent a genotype is expressed.
- Genes provide the blueprint for what an organism could grow up to be.
e.g. The colour of hydrangea flowers differs depending on the acidity of the soil it is planted in.
If the soil is acidic the pigment in the flowers will cause the flower to be blue. If it is an alkaline
environment, the flower colour will be pink.
There was a famous study 40 years ago, where two identical twins where adopted into
separate families and raised in different environments. The result was that the twins showed
substantial differences between their intelligence, personality, and even outward appearance
Maintaining A Balance - HSC Biology 2012 Notes
Peter Richardson
DNA Replication
Significance
- The DNA in a cell contains the genetic information to make an entire
organism. When a cell divides it takes with it an exact copy of the
genetic code of that organism. (mitosis)
- Without DNA replication genetic information would not be able to be
passed on from generation to generation.
The Process
- All about the structure, The DNA molecule is a “mirror-image”
template for the other. If you split a DNA molecule into 2 separate
strands, each strand can be used to build a new, complementary strand.
(Nitrogen bases ensure an exact copy)
There are about 20 Different amino acids
Protein Production
Polypeptides: Polypeptides are chains of amino acids.
Proteins are made up of one or more polypeptide
molecules. The amino acids are linked covalently by
peptide bonds.
The exact shape of the final protein depends on the
sequence of the amino acids. Amino acids can be attracted
or repelled from each other, so how the chain twists and
folds upon itself depends on exactly which ones are
located where.
The shape of the protein molecules is essential to itʼs
purpose and it correct functioning.
RNA: Ribonucleic Acid
ʻAnti-codonʼ
- The opposite bases
Loose amino acids are carried to the ribosome. The
Ribosome is the active site for protein synthesis.
DNA -> m-RNA -> T-RNA
Maintaining A Balance - HSC Biology 2012 Notes
Peter Richardson
•
Start & Stop Codonʼs - control the length of the peptide
chain. When the ʻstopʼ codon is reached, the polypeptide
chain is released into the cytoplasm.
•
Polypeptide synthesis involves a type of nucleic acid, called
RNA (ribonucleic acid). RNA is the intermediary between
DNA and polypeptide synthesis.
•
thymine, is replaced by uracil
Mutations & The Generation of New Alleles
Mutation is another way in which variation can
arise. If a mutation occurs in the production of
eggs / sperm (Meiosis), it will be passed down to
the next generation. If it occurs in the body cells
(through meiosis), it will effect only that organism.
Three things can happen as a result of a mutation:
1.
Beneficial
2.
Harmful
3.
Neutral (it won’t do anything)
The mutation causes a change in the code of the DNA (base sequences). This means that, possibly,
new amino acids will be introduced in polypeptide chains, this will lead to new proteins being
produced, and new forms of traits (alleles).
The real danger is from mutations that occur in the sperm and eggs
before you were even created, or early on after fertilization. These are
mutations that can be spread through the entire genome, as they are
the origins of YOU. And that’s how we have genetic disorders.
Some mutations do not have a clear cause (could be due to random
error). However, there are certain factors called mutagens that are
directly responsible for inducing a mutation.
Radiation was the first mutagenic factor to be discovered. In the 1920’s X-Ray’s were a great novelty and
were thought to be harmless) even being sold as an home entertainment device. (Note: Marie Curie died
of cancer as a result of working with radiation) Hans Muller received the Nobel Prize in 1927 for showing
that genes had the ability to mutate when exposed to X-rays. Today X-rays are used only with great care
and consideration, and handled safely in small amounts.
Ultraviolet Radiation
✤UV Radiation has been recorded to increase the incidence of skin cancer.
Radioactive Exposure / Radioactive Materials :
✤People who live in areas which have been affected by high-level radiation show a huge
increase in genetic mutations. (esp. after atomic bombs, or nuclear reactor disasters)
Maintaining A Balance - HSC Biology 2012 Notes
Peter Richardson
Beadle & Tatum - 1930ʼs & 1940ʼs
• They wanted to test the hypothesis (suggested by another scientist
earlier) that a gene is responsible for the production of a specific
protein (or enzyme).
• They hypothesized that it should be possible to create genetic
mutants that are unable to carry out specific enzymatic reactions.
• They exposed a bread mold (Neurospora) to X-ray’s to induce
mutations. The mutated mold has very specific nutritional needs. It
could not live without new added vitamins. Before, the bread mold only
needed one vitamin to stay alive! Why is this significant?
• Beadle and Tatum were able to create single gene mutations that stopped the proper function of specific
enzymes, so that the molds with these mutations required an external supply of the substance that the
enzyme normally produced. (their hypothesis was correct)
• This hypothesis used to be called the ‘One Gene - One Protein’ Hypothesis. However, this has since
been modified to the ‘One Gene - One Polypeptide’ Hypothesis. This is because genes code for
polypeptide chains that may not necessarily become enzymes, but many other kinds of proteins.
Modern Understanding & Darwinʼs Theories
The basis that Darwin’s theory of evolution relies upon is that of variation. Variation is key.
In Charles Darwin’s life time no one could explain where variation in a species came from, or how
characteristics where transferred from one generation to the next. However, with our current
understanding of genetics, we are able to appreciate, at a biochemical level, the importance of
variation in evolution.
Punctuate Equilibrium vs. Gradual Change
Darwin’s Gradualism
✦
✦
✦
Punctuated Equilibrium
✦
✦
He proposed that populations change
slowly and gradually over time
However, the fossil record only shows
rare occasions where this happens.
If an environment remains stable for
many years, we would expect there to
be no change in the organisms living
there. It is only when the environment
changes that natural selection occurs!
The fossil record in fact, shows periods of stability followed by a sudden change, and mass extensions.
Punctuated Equilibrium proposes that instead of gradual change, there have been periods of rapid
evolution followed by long period of stability, or equilibrium.
Maintaining A Balance - HSC Biology 2012 Notes
Peter Richardson
The Discovery of the Structure of DNA
James Watson & Francis Crick
✦
They suggested the double helix structure of DNA as well as the pairing of
the bases.
✦
They hypothesised that this structure aided in DNA replication.
Rosalind Franklin
✦
Provided crucial scientific evidence upon which Watson & Crick
based their double helix model. (Using X-Ray diffraction) The
images she took were very precise, using very thin strands of
DNA.
✦
Sexism was a trouble at the time. She did not collaborate well
with her partner Wilkins.
Maurice Wilkins
✦
Without permission, took Franklin’s famous X-Ray Diffraction
photo and passed it on to Watson & Crick.
Reproductive Technologies - Effect on Genetic Composition of Population
Generally, as a result of reproductive technologies, the genetic variation of populations tends to
be reduced (over many generations). Currently used for improved crop and livestock yields
(except cloning)
Artificial Insemination
- The injection the of male semen into a female.
- Taken from a male with desirable qualities.
- Easy to transport, and to inseminate many
females from one male.
Cloning
Artificial Pollination
- The pollination of plants (as Mendel did)
- Easy procedure.
- Cloning produces genetically identical copies.
- Plant cloning (cutting and grafting, also culture technology)
- Animal cloning (e.g. dolly the sheep)
1. Adult sheep tissue cell removed from sheep and cultured in lab
2. Nucleus removed from one of these cells and placed in an enucleated egg cell (egg
cell with genetic info removed)
3. Gentle electric pulse causes nucleus to fuse with egg cell
4. A second electric pulse starts cell division and embryo formation
5. This new cell is implanted into a female sheep where it grows into a new organism
Transgenic Species
Note: Biotechnology; Use of various techniques to change living organisms at the molecular level to
produce useful products or provide service.
Transgenic organisms contain a desired gene that has been transferred into their chromosomes from
another species. New DNA made by combining different DNA pieces is known as recombinant DNA.
1. A useful gene, and the chromosome it is on, is identified.
2. The gene is ‘isolated’ or cut-out of its DNA strand. (using restriction enzymes - The cut ends are
known as sticky ends)
3. Separate sequences may need to be added to ensure the gene will work.
4. The gene is inserted into the cell of another organism. Sometimes a vector is used to do this.
Maintaining A Balance - HSC Biology 2012 Notes
Peter Richardson
~~ On the DNA strands are also control or promoter sequences that switch the gene ‘on’ or ‘off’.
They regulate when a protein is made, how much is made, an in which cells the gene will function.
An isolated gene cannot function if it is transferred alone; it needs a promoter sequence to ensure
the gene will work.
~~ For genetic engineering to be possible on a large scale, multiple copies of genes need to be
made. Polymerase Chain Reactions (PCR) do this.
Example
The production of Bt crops
The use of Bt (a bacterium) in pesticide sprays is very successful at resisting insect attack.
Genetic engineering can eliminate the need to spray by inserting the Bt genes that produces
the Bt toxin directly into the plants.
The impact of this addition to the natural genetic variation in Bt crops is unknown.
Genetic Diversity
The main fear behind the use of genetic and reproductive breeding techniques on organisms
is that the natural diversity and variation within populations is decreased
E.g. cotton plants. The main crop being grown all over the world is BT cotton.
As more and more farmers shift from natural cotton to BT cotton, there are many
disadvantages:
-- Many natural varieties of cotton will be lost
-- The species itself becomes vulnerable to extinction. If all cotton grown all over the world is
BT, and a disease appears, that kills specifically BT cotton, than there is a risk of cotton
becoming an extinct organism
In another case, a population of cattle that have all been fathered by the same bull, through
artificial insemination techniques, is at risk to environmental changes
A lack of variation is a major risk factor in extinction of a species.
Ethical Issues
‣
‣
‣
‣
‣
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The companies who develop transgenic species own patents on them - making huge
profits.
Transferring genes, especially human, is seen as wrong religiously and morally.
Should we be tampering with nature in this way?
If a transgenic species was released into the natural environment, it could out-compete
the natural organisms
Health-risks and side effects with eating GM foods.
But also positive side.. Increase crop and livestock yield. Also these technologies help
treat diseases.