Transcript IB Biology - IBperiod5

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.
5.4.5 State the members of a
species show variation
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 nonresistant 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.