Evolution

• Biodiversity

  The combination of all life on earth: The plants and animals, the genetic information they contain and the ecosystems the live in and interact with
• Genetic diversity

  refers to the range of genes a particular species contains. Having a wide range of genetic diversity is important, as it allows a species to adapt to changing environments.
• Species diversity

  Refers to the variety of species that exist, each with its own genetic diversity within a habitat or ecosystem. Some ecosystems, such as a coral reef, have more diversity of species then others, such as a desert.
• Ecosystem diversity

  Refers to the variety of ecosystems that exist.. This is sometimes called functional diversity, as scientists study the function of each organism in its ecosystem.
• Evolution

  The change in gene frequency of a population
• Biodiversity as a function of evolution

  Biodiversity is increased by genetic change and evolutionary processes and reduced by habitat destruction, population decline and extinction.
• Causes of variation in a species

  The main causes of variation within a species are:

  • Independent assortment
  • Recombination (crossing over)
  • Mutations
• Independent assortment

  During meiosis the chromosomes move independently to the middle of the cell meaning that the chromosomes will make sex cells with different combinations of genes
• Recombination (crossing over)

  During meiosis, chromosomes of the same size and shape (homologous) exchange segments of their chromosome. The process results in chromosomes containing different combinations of genes.
• Mutations

  Random changes in the DNA sequence of an organism. They can occur when mistakes are made in copying the DNA. If the mutation is beneficial and occurs in the gametes then it can be passed onto offspring
• Effect of environment on phenotypes

  Environmental factors such as temperature can impact which of the organisms genes are expressed.
• Population

  The number of individuals of a species in a given place and time
• Gene pool

  The combination of all genes present in a population at a particular place and time
• Allele frequency

  How frequently a particular allele appears in a population
• Mechanisms of evolution

  The mechanisms that cause evolution in a population are:

  • Natural selection
  • Mutation
  • Gene flow
  • Genetic drift
• Natural selection

  The increase or decrease in an allele's frequency due to nature selecting for alleles based on how advantageous they are to the survival of an organism
• Gene flow

  An increase or decrease in an alleles frequency due to immigration or emigration of organisms
• genetic drift

  An increase or decrease in an alleles frequency due to a chance event or random mating
• Selection pressures

  The things that will stop an organism from surviving and reproducing. Eg:

  • Predators
  • Diseases
  • Temperature
• Processes required for a species to evolve due to natural selection

  Variation

  Isolation

  Natural selection

  Time
• Artificial selection

  Also known as selective breeding it is the intentional reproduction of individuals with desirable characteristics. It is when humans choose what nature should breed.Effects of selective breeding:

  Effects of selective breeding:

  • Frequency of desired trait increases
  • Decrease in genetic variation- more susceptible to disease
• Species

  A group of organisms that are capable of producing offspring which are then capable of producing offspring
• Speciation

  The formation of a new and distinct species in the course of evolution
• Steps towards speciation- Variation, overpopulation and competition


  Overtime population increases.

  Variation exists within the population

  There is a struggle for existence (increased competition) as resources become limited.

  Populations gradually move to different regions
• Steps towards speciation- Geographical barriers

  Overtime geological movement occurs resulting in a geographical barrier (eg: ocean, mountain range). This prevents gene flow and the populations become isolated.
• Steps towards speciation- Natural selection

  Different selection pressures (eg: climate) act on the populations. Different variations provide a different survival advantage within each population. This changes the allele frequency of the gene pool
• Steps towards speciation- Speciation and reproductive isolation


  The gene pool changes over time. Speciation occurs where the parent population evolves and become two new species. The species are now reproductively isolated.
• Fossils

  Preserved remains, impressions or traces of dead organisms
• Conditions to preserve a fossil

  The evidence must not be eaten or destroyed and then it must decay slowly
• Types of fossils

  The types of fossils are:

  • Body fossils: preserved remains of part of or the whole body of an organism
  • Trace fossil: the preserved evidence of an organism activity
  • Chemofossils: Preserved compounds produced by living organisms
  • Mould fossils: Imprint left in rock
  • Cast fossils: Imprint filled in by rock
• Fossil Dating

  Absolute dating is the process of determining how old a fossil is by looking at the radioactive material in the rocks and how much it has decayed.

  Relative dating: Deeper layers of rock are older and layers closer to the surface are younger
• Fossil records

  A list of all the organisms that fossil evidence has been found for. SHows that the number and type of species on Earth do not remain the same overtime and are increasing despite extinction events.
• Fossil evidence for evolution

  Fossils:

  1. Fossils show a clear transition from simple to complex life forms
  2. Fossils indicate that there has been a vast increase in biodiversity overtime
  3. Fossils have allowed scientists to approximate the first appearance of life on earth.
  4. Transitional fossils show the transition from one species to another
• Comparing DNA

  Comparing DNA sequences examines the relationship between different species. If the theory of evolution is supported then species that share a common ancestor will have inherited that ancestor's DNA sequence. The more alike the two DNA sequences are, the more closely related the two species are.
• Comparing amino acids in proteins

  Proteins are made from amino acids and the sequence of these amino acids is controlled by genes. Comparing how many of the amino acids are in the same position on the protein chain can provide some idea on how closely related the two species are.
• Homologous structures

  Similar features found in different species that have been inherited from a common ancestor. Many perform different functions.

  By identifying homologous structures we can identify related species. For example all mammals share the same arrangement of bones in their forelimbs. This is known as the pentadactyl limb and in each animal the bone structures are required for a different function. This means that all mammals have a common ancestor
• Analogous structure

  Structures in organisms that perform the same function but are structurally different. Organisms may come from different evolutionary backgrounds but develop similar features because they are subjected to similar selection pressures. This is an example of convergent evolution."

  Eg: Wings in birds and butterflies
• Vestigial structures

  Functionless structures found in organisms. They provide evidence for evolution because they suggest that an organism has evolved from using that structure to not using that structure.

  Eg:

  • Wisdom teeth
  • Apendix
  • Rear leg of snakes
• Embryology

  Comparative embryology involves looking at the similarities and differences between the embryos of different species.

  1. The structural similarity of embryos suggests that species have come from a common ancestor.
  2. The genetic similarity of embryos suggests species have common master genes inherited from a common ancestor.

  Embryos often possess structures that aren't present in the adult form. Many organism's embryos possess gills and tail-like structures even if they don't as adults. This allows us to identify the relatedness between species that look very different as adults.
• Biogeography

  The study of the Geographical Distribution of organisms