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Evolution (4.1 Evolution of Life (Evidence to support the evolution theory…
Evolution
4.1 Evolution of Life
Evidence to support the evolution theory of endosymbiosis:
- mitochondria and chloroplast have their own DNA, separate from the nucleus and similar to prokaryotic DNA (circular).
- mitochondria and chloroplast have their own ribosomes, which resemble bacterial ribosomes.
- mitochondria and chloroplast are able to self-replicate in a process similar to binary fission.
- mitochondria and chloroplast have a double membrane.
Comparative genomics provides evidence for evolution and helps establish the likely evolutionary relationship between different species.
Fossil evidence suggests that life appeared 3.5 billion years ago, with anaerobic prokaryotes as the first cells on Earth. This is due to the reasoning that the earths early atmosphere contained no oxygen and large amounts of carbon dioxide and nitrogen, not suitable for eukaryotic cells.
Techniques for obtaining evidence:
- Amino Acid Sequencing - the amino acid sequence of proteins is compared between two species. Closely related species have a greater number of similarities in the amino acid sequence of proteins.
- DNA Hybridisation - the DNA of two different species is heated so that their strands separate. Upon cooling the single strands of DNA recombine. The better the match of nucleotide bases, the more closely related the two species are.
- DNA Sequencing - the actual sequencing of bases in a specific gene is determined. Closely related species have a greater number of similarities in the DNA sequence of a gene.
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The role of RNA in the first cells was to store and transmit genetic information.
The role of ribozymes in the first cells was to catalyse metabolic reactions.
Membranes may have formed spontaneously and the first simple cells may have used RNA as genetic information. Ribozymes may have played a role in this development.
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More closely related species have fewer differences in their DNA sequences and have separated more recently than distantly related species.
Evidence shows that life has existed on Earth for around 3.5 billion years, during which time it has diversified.
4.4 Speciation
Examples of Convergent Evolution:
- Bats & Birds (wings)
- Dolphins & Sharks (body shape)
- Bees, Butterflies & Moths (tongue and beak)
When new niches become available to a species, for example as a result of succession or following an environmental change, different selection pressures may lead to divergent evolution or adaptive radiation.
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Examples of Adaptive Radiation (divergent evolution):
- Galapagos Finches
- Marsupials of Australia
- Placental Mammals in Australia
Allopatric speciation occurs when a population is separated by a geographical barrier, whereas sympatric speciation occurs when a population gives rise to two new species while still inhabiting the same region.
Succession is the gradual process by which the species composition within a given geographical location changes. This may be brought about by modification of the environment caused by organisms that live within the area.
Allopatric speciation occurs when a population is separated by a geographical barrier, which prevents interbreeding and gene flow between the two populations. With the two populations being subjected to different biotic and abiotic factors, they are exposed to different selection pressures, therefore resulting in natural selection and genetic drift occurring, and thus leading to a change in gene frequency and reproductive isolation. As a result, the two populations can no longer produce fertile offspring and are now considered different species.
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Speciation may result from an accumulation of genetic changes influenced by different selection pressures or genetic drift in geographically isolated populations.
Species with low genetic diversity:
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