Lecture 3 : Evolution Etc' Overview

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Lecture 3 Evolution Etc.Overview

• MEIOSIS AND INHERITANCE
• Meiosis
• Sexual Reproduction
• Dominant and Recessive Genes
• Mutations
• EVOLUTION
• INFECTIOUS DISEASES
• Parasitism
• Pathogenic Factors

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Meiosis

• Meiosis is a complex process involving two cell
  divisions. It produces 4 sex cells (or gametes)
  from each original cell.
• Each gamete contains a half set of chromosomes
  (23 in the case of humans).
• DNA is exchanged between chromosomes during
  meiosis, in a process known as crossing over,
  resulting in greater genetic diversity.

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Sexual Reproduction

• Fertilisation occurs when a gamete produced by a
  male (sperm) fuses with a gamete produced by a
  female (ovum) to create a zygote with a complete
  set of chromosomes half from each parent.
• The embryo develops from the zygote through
  mitosis.
• Following meiosis, each of the four egg cells
  from the female always contains an X chromosome,
  whereas two of the sperm cells from the male will
  contain an X chromosome and two will contain a Y
  chromosome. The sex of the offspring is therefore
  determined by the type of chromosome passed on by
  the father via the fertilising sperm cell.

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Dominant And Recessive Genes

• Each person has two sets of chromosomes 23 from
  their mother and 23 from their father and
  therefore 2 sets of genes.
• Each person may therefore have conflicting genes
  coding for a particular function.
• One gene may become dominant, and the other is
  recessive.

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Mutations

• DNA may be damaged during replication or by
  external influences resulting in a mutation.
• The effects of mutations may be positive,
  negative or neutral.
• Mutations in sex cells can be transmitted to the
  next generation mutations in other cells cannot
  be transmitted.

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Evolution

• Jean-Baptiste Lamarck (1744-1829) was an early
  proponent of evolution.
• Charles Darwin (1809-1892) introduced the notion
  of natural selection in 1848.
• Diversity within a species is introduced by
  mutations organisims which are best suited to
  their environment will survive in greater numbers
  to transmit their genes to the next generation
  survival of the fittest.
• The peppered moth (Biston betularia) provides an
  excellent 19th century example.

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Biston betularia f. typica
Biston betularia f. carbonaria
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Importance Of The Environment

• Natural selection means that most species are
  well adapted to their environment.
• In most situations new mutations are unlikely to
  enhance the fitness of species.
• The exception is when there is a change in
  environment which may confer an advantage on the
  mutations.
• To understand evolution, it is therefore
  necessary to understand environmental changes.

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Infectious Diseases

• Most infectious diseases are caused by a
  particular species of microorganism (or microbe),
  but some larger organisms also cause disease.
• Microorganisms are ubiquitous. Only a small
  minority of microorganisms are pathogenic (i.e.
  disease causing).
• Pathogens do not have malicious intent. Jacques
  May (1950) diseases are merely the by-product
  of an accidental collision between two or more
  forms of life, each pursuing its own destiny.

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Parasitism

• Only a minority of microorganisms are parasitic,
  but all pathogens are parasitic.
• A parasite is an organism that lives on or in
  another organism (referred to as the host) and
  depends upon it for nutrition, often to the
  detriment of the host.
• Parasitism is a form of symbiosis (living
  together).
• Other forms of symbiosis include commensalism and
  mutualism.
• Parasites tend to be particularly well adapted to
  specific hosts.

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Pathogenic Factors

• 1. Hosts - the human (or other organism)
  infected.
• 2. Causal agents the organism that causes the
  disease.
• 3. Vectors organisms (usually an arthropod)
  which transmit the causal agent from one infected
  host to a new host.
• 4. Intermediate hosts - organisms (usually
  molluscs, fish or mammals) which are essential to
  the life cycle of the causative agent.
• 5. Reservoirs other species which act as a host
  to the causal agent.

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Disease Prevention

• All infectious diseases require at least two
  factors (host agent).
• Many require additional factors (i.e. vector,
  intermediate host, or reservoir).
• Each factor has its own geography. These
  geographies must overlap for the disease to be
  present.
• Diseases may be prevented by eliminating one of
  the factors.
• This is not only difficult, but it may have
  unforeseen ecological consequences.