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What is Evolution?

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Jesse Bowcock

on 4 November 2013

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Transcript of What is Evolution?

Natural Selection
What is it? When something changes
into something else over time
Passing on genetic
Natural selection is the gradual natural process by which biological traits become either more or less common in a population as a function of the effect of inherited traits on the differential reproductive success of organisms interacting with their environment. It is a key mechanism of evolution. The term "natural selection" was popularized by Charles Darwin who intended it to be compared with artificial selection, which is now called selective breeding.
Types of Selection
Evidence for Evolution
Stabilizing selection
The medium has the hightest survival rate whereas the other two extremes experience selective pressure.
Directional Selection
One extreme is favored against the other extreme, resulting in selective pressures.
Disruptive selection
If one extreme isn't adapting to the surrounding then the survival rate decreases, whereas the other two extremes will keep increasing
Types of evolution
Convergent evolution
Convergent evolution is the process where organisms not closely related (not monophyletic), independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. Opposite of Divergent evolution where a related species will develop different traits. Convergent evolution can happen in different ways, on a molecular level it can occur due to a mutation in the genes, or in some cases the development of similar cultural adaptations to similar environmental conditions by different peoples with different ancestral cultures. An example of Convergent evolution is the wings on a bird, insect and bat. All serve the same function but have evolved independently.
Divergent Evolution
Divergent evolution is when one species evolves into two separate species due to geographic separation followed by different selection pressures on each of the populations (see types of selection). The vertebrate limb is one example of divergent evolution as the limb in many different species has a common origin, but has diverged somewhat in overall structure and function. In the case of divergent evolution, similarity is due to the common origin, such as divergence from a common ancestral structure or function has not yet completely obscured the underlying similarity. In contrast, convergent evolution arises when there are some sort of ecological or physical drivers toward a similar solution, even though the structure or function has arisen independently.
The y chromosome emerged around 200 to 300 million years ago, in a common acestor of most mammals. Males and females did exist, but their sex was determined by environmental factors such as temperature, rather than gentics.

In mammals, the y chromosome contains the gene SRY, which triggers the development of testicles. When an ancestral mammal developed an allelic variation, a so called 'sex-locus' causing the organism to be male. Overtime, genes which were beneficial for males and harmful to females either developed the y chromosome, or were acquired through the process of translocation.
The Y Chromosome
In 2002, an article in 'Nature,' two Australian scientists examined the rate at which the Y chromosome has withered and estimated that it will 'self-destruct' in around 10 million years. As the Y chromosome doesn't exist anymore in rats or moles.
Theories of evolution
Use and disuse
The evolution of the Y chromosome
Evolution and selection pressures
The theory of use and disuse of Jean-Baptiste Lamarck, advocated the idea that animals acquired characteristics after using certain physical traits constantly. For example, he believed that the reason why the necks of giraffes were long was because they stretched to reach leaves on high trees.
Fossils are the preserved remains or traces of animals, plants, and other organisms from the remote past.
Formation of fossils
Analogous and Homologous features
Analogous features in different organisms have the same function but have evolved independently. They are evidence of convergent and parallel evolution.
Homologous features are evidence of divergent evolution—splitting of a common ancestral species into two new different species.
Fossilisation occurs when a shell, for example, is buried and entombed by sediments. Sediments of sand, silt or mud in the sea, a lake or slow- flowing stream, accumulate over the shell, and protect it from later erosion. The weight of many layers of sediments squeezes out water between the particles of sand, silt or mud. As the deposit deepens, the temperature increases and soft sediments become solid rock—sandstone, siltstone, mudstone or shale (a mixture of clay and silt). Fossils are also formed during the formation of coal, when plant debris accumulates in swamps
Population is the number of
organisms of which can reproduce
Allele Frequency
Sexual Selection
Nonrandom mating
Gene Flow
Genetic Drift
Alleles for fitter organisms become more frequent
Changes in allele frequency due to random chance
Changes in allele frequency
Specific traits and changes in genetic makeup
New allele popping up,
and error or mistake
Some mutations
are beneficial
No all mutation
are harmful
Frequency of alleles remains constant from generation to generation

Hydrogen Bonding
Hydrogen Bonding is a chemical interaction that underlies the base-pairing rules.
The insertion or deletion of a number of bases that is not a multiple of 3. This alters the reading frame of the gene and frequently results in a premature stop codon and protein truncation.
Cytosine and Guanine is a form of triple hydrogen bonding, creating a 1:1 ratio of pyrimidines
A change in the genetic code that results in the coding for a stop codon rather than an amino acid. The shortened protein is generally non-function or its function is impeded.
Adenine and Thymine produce a double hydrogen bond forming a 1:1 ratio of purines
When genetic material is put into another region of DNA. This may be the insertion of 1 or more bases, or it can be part of one chromosome being inserted into another, non-homologous chromosome.
Genetic material is removed or deleted. A few bases can be deleted (as shown on the left) or it can be complete or partial loss of a chromosome
A change in the genetic sequence that does not change the protein sequence. This can occur because of redundancy in the genetic code where an amino acid may be encoded for by multiple codons.
A mutation is a permanent change in the sequence of DNA. In order for an observable effect, mutations must occur in gene exons or regulatory elements. Changes in the non-coding regions of DNA (introns and junk DNA) generally do not affect function.
What is a mutation?
What causes mutations?
Mutations can be caused by external (exogenous) or endogenous (native) factors, or they may be caused by errors in the cellular machinery. Physical or chemical agents that induce mutations in DNA are called mutagens and are said to be mutagenic.
Exogenous factors: environmental factors such as sunlight, radiation, and smoking can cause mutations.
Endogenous factors: errors during DNA replication can lead to genetic changes as can toxic by-products of cellular metabolism.
Impact of a mutation
Mutations can be advantageous and lead to an evolutionary advantage of a certain genotype. Mutations can also be deleterious, causing disease, developmental delays, structural abnormalities, or other effects.
Chargaff's Rule
states that DNA from any cell of all organisms should have a 1:1 ration of pyrimidine and purine bases

Hardy-Weinberg's Theorem

In translation, the messenger RNA (mRNA) produced by transcription is decoded by a ribosome complex to produce a specific amino acid chain, or polypeptide, that will later fold into an active protein.

Protein Synthesis
Protein synthesis is accomplished through a process called translation. After DNA is transcribed into a messenger RNA (mRNA) molecule during transcription, the mRNA must be translated to produce a protein. In translation, mRNA along with transfer RNA (tRNA) and ribosomes work together to produce proteins.
Transfer RNA
Transfer RNA plays a huge role in protein synthesis and translation. Its job is to translate the message within the nucleotide sequence of mRNA to a specific amino acid sequence. These sequences are joined together to form a protein. Transfer RNA is shaped like a clover leaf with three loops. It contains an amino acid attachment site on one end and a special section in the middle loop called the anticodon site. The anticodon recognizes a specific area on a mRNA called a codon.
Messenger RNA modifications
Translation occurs in the cytoplasm. After leaving the nucleus, mRNA must undergo several modifications before being translated. Sections of the mRNA that do not code for amino acids, called introns, are removed. A poly-A tail, consisting of several adenine bases, is added to one end of the mRNA, while a guanosine triphosphate cap is added to the other end. These modifications remove unneeded sections and protect the ends of the mRNA molecule. Once all modifications are complete, mRNA is ready for translation.
How it works
Difference Between Translation and Transcription

Transcription: the process of copying the gene’s DNA into RNA.
Translation: the process of using RNA to synthesize protein.

Stage 1: Initiation
Stage 2: Elongation
Stage 3: Termination
Transcription factors bind the promoter region of a gene. The promoter region indicates the beginning of gene, the start point for transcription. RNA Polymerase, the molecule responsible for copying the DNA into RNA, binds to the complex of transcription factors at the promoter. Working together, RNA Polymerase and the transcription factors start to unwind the DNA double helix and RNA synthesis begins.
RNA Polymerase unwinds the DNA double helix and moves downstream and elongates the RNA transcript by adding ribonucleotides in a 5’-->3’ direction. Each ribonucleotide is added to the growing mRNA strand using the base pairing rules (A binds with T, G binds with C). For each C encountered on the DNA strand a G is inserted in the RNA, for each G, a C and for each T, an A. Since there is no T in RNA, U is inserted whenever an A is encountered.
When the RNA Polymerase reaches the terminator region (the end of the gene), the mRNA transcript is released and the polymerase detaches from the DNA.
What is Replication?
Each time a cell divides, the two resulting daughter cells must contain the same genetic information, or DNA. Each strand of existing DNA acts as a template for replication. There are three major steps to replication;
The opening of the double helix and the separation of the DNA strands
The priming of the template strands and;
The assembly of the new DNA segment.
Two strands of DNA double helix uncoil at the origin
Enzymes and proteins then prepare the strand for duplication
Enzyme called DNA polymerase organises the assembly of new DNA strands
Initiation of DNA replication
The indicator protein unwinds a short stretch of the DNA double helix. The protein Helicase attaches and breaks apart the hydrogen bonds between the bases on the DNA strand, breaking apart the two DNA strands. Moving along the DNA molecule, the helicase continues breaking these hydrogen bonds and separates the two polyneuleotide chains. The enzyme primase will then briefly attach to each strand and assemble a foundation at which replication can begin.
After the primer is placed on the unwound polyneucleotide strand DNA polymerase wraps itself around the strand and attaches new neucelotides to the bases. Polymerase then assembles a new DNA strand on top of the existing one. Neucleotides that make up the new strand are then paired with partner neucleotides in the template strand because of their molecular structures. A & T always pair and C & G always pair . This is known as "complementary base pairing".

Complementary base pairing
Base pairing ensures that the sequence of neucleotides in an existing template strand is exactly matched to a complementary sequence.As a result of complementary base pairing the coding of original DNA is preserved. If an error occours during replication (e.g. A & G join) a mutation will occour and continue to mutate.
Having different alleles
at a particular genetic locus,
for example Aa

Having two identical alleles at a particular genetic locus, for example AA
Monohybrid Cross
Cross involving the segregation of the allelels of a single gene

Dihybrid Cross
Cross involving the segregation of alleles of two genes; a dihybrid is an individual that is heterozygous at two different loci, for example Aa; Bb

1) Character or observable trait of an organism
2) The overall apperance of an organism

The total set of genes in an organism
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