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Genetics and Evolution (Antibiotic-resistant Bacteria (Bacteria can evolve…
Genetics and Evolution
The history of Genetics
In the mid 19th century, gregory mendel carried out breeding experiments on plants, one of his observations was that the inheritance of each charateristic is determined by 'units' that are pased on unchanged to descendents.
In the late 19th century the behaviour of chromosomes and Mendels units behaved in similar ways. This lead to the idea that the units now called genes were located on the chromosomes
In the mid 20th century the structure of DNA was determined and the mechanism of gene function was worked out
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Theories of Evolution
Earlier theories of evolution including that of Jean Baptiste Lamarck are based mainly on the idea that changes that occur in an organsim during its lifetime can be inherited. We now know that in the vast majority of cases this type of inhertance cannot occur.
Charles Darwin proposed his theory of evolution by natural selection largely as a result of observations made on a round the world expedition.
The individual organsims in a particular species tend to show a wide range of variation for each characteristic
Reproduction always gives more offspring that the environment can support. The organisms that have inherited the characteristics most suited to their environment - the 'fittest' - are more likley to survive and breed successfully
When they breed, they apss on the characteristics that have enabled them to survive to the next generation.
Accepting Darwin's Ideas
Darwins theory of evolution by natural selection was only gradually accepted for a number of reasons. These include conflict with the widely held belief that God made all the animals and plants, insufficient evidence, and no mechanism for explaining variety and inheritance which would not be understood for another 50 years.
Evolution and Speciation
Alfred Russel Wallace independently proposed the theory of evolution by natural selection. He published join writing with Darwin in 1858, which prompted Dawrin to publish The Origin of Species the following year (1859)
Wallace worked worldwide gather evidence for evolutionary theory. He is best known for his work on warning colouration in animals and his theory of speciation.
Build up of evidence of time has led to our current udnerstanding of the theory of speciation. New species arise as a result of: isolation: where two populations of a species become separated, genetic vatiation between the populations, natural selection that operated differently on the two populations, and speciation: wehre the populations become so different that interbreeding is no longer successful
Evidence ofr Evolution
Fossils are the remains of organisms from millions of years ago that can be found in rocks ice and other places
Fossils may be formed in different ways including the absence of decau, parts replaced by other materials as they decay and as preserved traces of organisms.
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It is very difficult for scientists to know exactly how life on Earth began because there is little valid evidence. Early forms of life were soft bodies so left few traces behind and many traces or early life have been destryoed by geological activity
Fossils and Extinction
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Extinction maybe be caused by by a number of factors including new predators new diseases or new more successful competitors
More About Extinction
Extinction can be used by a variety of factors including changes to the environment over geological time and single catastrophic events such as massive volcanic eruptions or collisions with asteroids
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Clasification
Traditionally living things have been clasified into groups depending on their structures and characteristics in a system described by Carl Linnaeus
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As evidence of the internal structures of organsism because more developed due to improvements in microscopes and the understanding of biochemical processes pregressed new models of classification were proposed
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