evolution and genetics 12-13 handout 2 slides per page
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Evolution and GeneticsTRANSCRIPT
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Biological Psychology
DNA, Genetics & Evolution
Is this what makes you human?
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Chromosomes
Each chromosome is a double stranded molecule of deoxyribonucleic acid (DNA).
The structure of the molecule was described in 1953 by James Watson and Francis Crick.
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DNA
The two strands are held together by nucleotide bases which are attracted to each other.
So that:
Adenine links to Thymine
Guanine links to Cytosine
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So what are genes?
Genes are sequences of nucleotide bases.
Imagine a simple alphabet made up of only 4 letters
A, T, C, G
Genes are words made up of sequences of these bases
Interesting Facts
It has been estimated that the human genome (the total complement of all 23 pairs of chromosomes) contains over 3,000 million base pairs (A-T, C-G).
To enable over 3,000 million base pairs to exist, each cell in the body contains about 6 feet of DNA crammed into a nucleus that is 0.005mm in diameter.
It is estimated that our 23 pairs of chromosomes contain around 30,000 genes.
This is the amount of information required to build a human being from a single egg and to maintain it through life.
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The Importance of DNA
Genes provide a code to make amino acids.
Amino acids are the building blocks of proteins.
Our genes can only make 20 different amino acids.
All our proteins are made from these 20 amino acids
DNA and Proteins
So:
The instructions for making proteins are stored on chromosomes locked away in the cells nucleus.
However, protein manufacture does not take place in the nucleus, but in the surrounding cytoplasm. How?
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The Answer
Thanks to another nucleic acid ribonucleic acid (RNA).
Similar to DNA, but it exists as a single strand, enabling it to move in and out of the nucleus.
Has the base URACIL instead of thymine.
The Process
MESSENGER RNA (mRNA) transports the DNAs instructions from the nucleus to the cytoplasm.
The genes are translated into amino acids.
Each amino acid is added to a lengthening strand.
When the length of the mRNA is finally translated, the completed protein is released.
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Why are proteins important?
They are vital constituents of all living things.
A typical mammalian cell may have as many as 10,000 different proteins, each with its own unique role.
One of the most important roles of proteins is as enzymes
Where do we get our DNA from?
DNA is passed on from parent to child.
But you do not get all your parents DNA, you get half from you mother and half from your father.
This allows you to have different combinations of genes than your siblings.
This allow for variation between and within species.
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Human Reproduction
Humans have 23 matched pairs of chromosomes in the nucleus of all cells with one exception
The Egg and Sperm Cells
DIPLOID CELLS
46 chromosomes (most cells in the body)
HAPLOID CELLS
23 chromosomes (the egg in the female, sperm in the male)
Human Reproduction
Diploid cells replicate by a process called MITOSIS
Mitosis generates a complete copy of the cells genetic information
All new cells contain copies of all 23 matched pairs of chromosomes.
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Human Reproduction
Haploid cells (sperm and egg) are created by a process celled MEIOSIS
Only half the number of chromosomes
1 of each rather than 2 are assigned to each cell
The chromosome are randomly assigned to each gamete
Human Reproduction
When the sperm fertilises an egg, chromosomes from the mother pair up with the relevant partner chromosome from the father.
Therefore the resulting offspring inherits half its genetic information from its mother and half from its father.
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Human Reproduction
Why is this important?
VARIATION
New gene combinations are constantly produced.
No two individuals are the same.
Is this always true?
Genes and Chromosomes
Genes are located on CHROMOSOMES, which are present in the nucleus of every cell.
Chromosomes occur in matched pairs.
The 2 genes (alleles) that control each trait are situated at the same locus on each chromosome of a particular pair.
Each species has a characteristic number of pairs of chromosomes in each of its body cells.
How many pairs of chromosomes do humans have?
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A bit more variation
Variation is further promoted by the phenomenon of crossing over.
This occurs during meiosis.
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Mendel 1822-1884
Published his work in 1866.
In his revolutionary work, he did not deal with variation, but rather consistent traits.
He showed that traits can be passed from Grandparent to offspring, bypassing the parental generation.
He showed that traits were carried through something other than blood as had been assumed.
We will consider the work of Mendel in the seminar
Charles Darwin
Not a natural Biologist.
Not a natural academic.
But now known as the founder of modern day biology.
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Pre-Darwinian Thought 19th Century Britain
Creationism was accepted unchallenged by the general public
However, much of the evidence Darwin used to develop his theory was known
Geologists and Palaeontologists had evidence that life had existed on Earth for a long time AND that it had changed over time.
Members of a species look similar to each other when compared to another species.
BUT when compared to each other, there are differences between members of a species.
Theory of Inheritance of Acquired Traits
Jean-Baptiste Lamarck (1744-1829)
Suggested that the giraffes neck grow because the muscles in the parent stretch as it reached for food and that this trait was passed on to the offspring.
This is now disregarded as we know that only sperm and egg cells can pass on information.
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Charles Darwin (1809 1882)
Darwin returned from his world trip on the Beagle in 1837
By 1838 he had developed his theory of Evolution
Alfred Russell Wallace independently developed the same theory
In 1859 Darwin published his book On the Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life. Known As Origins of the Species
Darwins Theory
Evolution decent with modification
Evolution has occurred by branching so that different species share common ancestral species.
Natural Selection
The main mechanism of evolution. This is where random changes to an individual occur. Those which are beneficial will be passed on to the next generation.
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Natural Selection Members of a species vary greatly in their structure,
physiology and behaviour, traits that are associated with survival are more likely to be passed onto the next generation. Therefore natural selection leads to the evolution of species which are better able to surviving and reproducing in their particular environment.
The Reaction Caricature in Hornet taken from
http://en.wikipedia.org/wiki/Charles_Darwin
Is evolution universally accepted now?
Do YOU accept the theory of evolution?
Have you examined the evidence for evolution?
http://news.bbc.co.uk/1/hi/education/7612152.
stm
http://news.bbc.co.uk/1/hi/education/7619670.stm
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1. Darwins Evidence
He documented the evolution of fossil records through progressive geological layers
2. Darwins Evidence Taken from Carlson (2001) Physiology of Behaviour
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3. Darwins Evidence
Darwin argued that if dogs and horses could be bred to produce offspring with desirable characteristics, then why could this not happen naturally.
NATURAL SELECTION
Further Evidence
Science has moved on since Darwin. Can you think of any other ways of testing the theory of evolution?
Remember Darwin did not know about how information was passed on from parents to offspring. He had not seen the work of Mendel.
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Example of Natural Selection The Case of the disappearing (white) English Peppered
Moth
KEY FACTS
The English Peppered Moth (Biston Betularia) is whitish with black speckles on its wings.
They are camouflaged on speckled lichen on trees.
A genetic mutation can cause some moths to be all black, these are said to be melanistic.
Melanistic moths not camouflaged on lichen.
1800s Industrial Revolution.
Lichens sensitive to air pollution and die.
Black soot turns trees black
Example of Natural Selection And the White Moths Disappeared.
What has caused this mysterious disappearance? The white moths, no longer have an advantage and are being eaten.
The Black moths have an advantage and are not been eaten, so are able to reproduce and pass on the mutation.
There were however white moths in the countryside.
In the 20th Century The Clean Air acts, changed the environment again.
The white moths re-appear
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Survival of the Fittest The individual best suited to their
environment will survive to pass on these genes to the next generation.
This is a phrase coined by Herbert Spencer and was used to justify Social Darwinism.
Human Evolution: A big brain? Adult human brain weighs between 1200g and
1400g
Adult elephant brain weighs between 5,000g and 8,000g
Brain Body Ratio Humans 2.33%
Elephant 0.2%
Shrew 3.33%
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Human Evolution
Kingdom Animal
Phylum Chordate
Class Mammal
Order Primate
Family Hominid
Genus Homo
Species Sapiens
The Ape who Evolved to be Human
What key factors separate humans and apes?
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Human Evolution
From Kenyon http://www.flyfishingdevon.co.uk/salmon/
Evolutionary Psychology
Explains human behaviour in terms of evolution.
Darwin himself believed that human behaviour could be explained in terms of evolution.
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Whose Genes?
From Kenyon http://www.flyfishingdevon.co.uk/salmon/
Evolution Facts Evolution is not a straight line
Evolution does not progress to preordained perfection
Humans are the last surviving species of a family that has existed for a very short time
Evolution can be rapid
Fewer than 1% of known species are in existence
Not all existing behaviours or structures are adaptive
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Conclusion
Darwin developed his theory of evolution to explain the diversity that he saw around him
DNA was identified by Watson and Crick in the 1950s
Traits are passed from one generation to the next by genes located on chromosomes
We now understand that many human traits involve many genes (Polygenic)
And genes often provide just a predisposition to a condition or trait.