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IB Biology. 5.4 Evolution Lara Geis 2007-2008. 5.4.1 Define Evolution. Evolution is the cumulative change in the heritable characteristics of a population

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IB Biology

5.4 Evolution

Lara Geis 2007-2008

5.4.1 Define Evolution

  • Evolution is the cumulative change in the heritable characteristics of a population

  • If we accept not only that species can evolve, but also that new species arises by evolution from pre-existing ones, then the whole of life can be seen as unified by its common origins

  • Variation within our species is the result of different selection pressures operating in different parts of the world, yet this variation is not so vast to justify a construct such as race having biological or scientific basis

5.4.2 Outline the evidence for evolution provided by the fossil record, selective breeding of domesticated animals and homologous structures

Fossil Record:

The existence of fossils is very difficult without evolution. The Acanthostega is a 365 million year old fossil. It has similarities to other vertebrates with a back bone and four limbs, bit is has eight fingers and seven toes, so its not identical to any existing organism. This suggests vertebrates and other organisms can change over time.

Selective Breeding: Cows produce milk for ten months after calving. This period is called lactation. Fifty years ago about 400kg of milk was produced per lactation. As a result of breeding programs cows can now produce 8000kg per lactation. The cows with the highest yield of milk and are artificially inseminated with bulls who have been genetically tested and are predicted to produce the most yield.

Homologous Structures: At an early stage, vertebrate embryos are very similar, despite differences in the adult. The limbs of vertebrates show striking similarities in the bones. The most likely explanation for these structural similarities is that the organisms evolved from a common ancestor. Structures that have developed from a same part of a common ancestor are called homologous structures.

5.4.3 State that populations tend to produce more offspring than the environment can support

Populations tend to produce more offspring than the environment can support

5.4.4 Explain the consequence for overproduction of offspring is a struggle for survival

When a population overproduces offspring the consequence is that the environment can reach Carrying Capacity: the maximum population size that an environment can support.

Members of a species show variation

5.4.5 State the members of a species show variation

5.4.6 Explain how sexual reproduction promotes variation in a species

Variation is essential for natural selection and therefore for evolution. Although mutation is the original source of new genes or alleles, sexual reproduction promotes variation by allowing the formation of new combinations of alleles. Two stages in sexual reproduction promote variation

1. Meiosis allows a huge variety of genetically different gametes to be produced by each individual

2. Fertilization allows alleles from two different individuals to be brought together in one new individual

Prokaryotes do not reproduce sexually but have other ways to promote variation by exchanging genes

Some species of organisms only reproduce asexually. Mutations still produce some variation in these

species, but without sexual reproduction the variation and the capacity for evolution is less.

5.4.7 Explain how natural selection leads to evolution

Greater survival and reproductive success of individuals with favorable heritable variations can lead to change in the characteristics of a population

5.4.8 Explain two examples of evolution in response to environmental change

Multiple Antibiotic Resistance In Bacteria

  • Antibiotics are used to control diseases caused by bacteria in humans. There have been increasing problems with disease causing bacteria being resistant to antibiotics.

  • Genes that give resistance to an antibiotic can be found in micro organisms that naturally make that antibiotic. The evolution of multiple antibiotic resistance involves the following steps

    • A gene that gives resistance to an antibiotic is transferred to a bacterium by means of a plasmid or in some other way. There is then variation in the type f bacterium- some of the bacteria are resistant to the antibiotic to control bacteria.

    • Doctors or vets use the antibiotic to control bacteria. Natural selection favors the bacteria that are resistant to it and kills the non resistant ones.

    • The antibiotic resistant bacteria reproduce and spread, replacing the non-resistant ones. Eventually, most of the bacteria are resistant.

    • Doctors or vets change to different antibiotics to control bacteria. Resistance to this soon develops, so another antibiotic is used, and so on until multiply resistant bacteria have evolved

5.4.8 Example 2

Metal Tolerance In Plants

Waste materials from the mining of metal ores and smelting often contains high levels of metal such as lead, nickel, or copper. These wastes are often dumped and because of the metal pollution few plants grow on it. Some plants do colonies the waste heaps and when they are tested they are found to have higher tolerance to the metals in the waste than usual for their species.

Evidence for the evolution of metal tolerance in a grass ( Agrostis tenuis) was obtained in the following way.

An area of copper pollution around an old copper mine in North Wales was mapped.

A transect line was marked out which ran from an unpolluted area to a heavily polluted area

Samples of Agrostis tenuis plants were collected along the transect line and were tested for copper tolerance

Seeds were collected from the same plants. The seeds were collected from the same plants. The seeds were germinated and the plants that grew from them were also tested for copper tolerance.

The plants growing in the polluted area were more copper tolerant than the plants in the unpolluted area

The offspring in these plants inherited at least some of the copper tolerance , showing that genes are involved.

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