Inheritance, variation & evolution

• Variation may be a result of differences in:

  Environment

  Genetics
• Evolution is the gradual change of the inherited characteristics of biological populations over time.
• In natural selection:

  Individuals display genetic variation

  The characteristics that maximise survival chances are passed on

  Those with the best characteristics are more likely to breed.
• Adaptation is a characteristic that helps an organism to have a better chance of survival in its environment.
• Some adaptations help organisms to not get eaten, hide, control body temperature or prevent water loss.
•  Speciation happens when two animal populations diverge (separate or split) a lot.
• When speciation happens:

  Fertile offspring are not produced when different individuals are bred together

  Different species are formed
• Selective breeding (artificial selection) happens when humans choose animals and crops to breed, based on their genetic characteristics.
• Many different organisms are used in selective breeding. They include farm animals and crops.
• Steps for selective Breeding:

  • Choose parents who most strongly display the desired characteristic.
  • Breed the chosen parents.
  • From the resultant offspring (children), choose the offspring that best display the desired characteristic.
  • Breed these chosen offspring.
  • Repeat this process of breeding and re-selection over many generations until all the offspring show the desired characteristic.
• Usefulness and appearance are the two most common reasons for a characteristic being considered desirable. Some useful examples are:


  Dogs

  Animals

  Crops
• Selective breeding can create some problems:

  Inbreeding

  Reduced Variation
• Selective breeding can lead to inbreeding which means that some breeds can become susceptible to disease or inherited disease.
• Example of inbreeding is the French bulldog have been selectively bred to have a flat face. This causes breathing problems.
• Another problem with selective breeding is reduced genetic variation within populations. The population becomes less able to adapt to changes in its environment.
• What term is used to describe the reproduction of animals that are related to each other?

  Inbreeding
• Genetic engineering involves modifying (changing) an organism’s genome by introducing a gene from another organism to produce a desired characteristic.
• Examples of genetic engineering are:

  Vitamin A rice

  Insulin producing gene
• Some plants are genetically modified (GM) which means they have been engineered to have the following characteristics:

  resistance to insects and diseases
• Advantages of genetic engineering:

  Preventing inherited diseases

  Improving food production efficiency
• GM crops generally have higher yields than normal crops. They could be a solution to providing the nutrients that many people in developing nations do not consume. Golden rice is an example of this: it helps reduce Vitamin A deficiency.
• Since genetic engineering is a relatively recent development, it is uncertain what the long-term effects may be.
• Bacterial DNA has been engineered in such a way that it incorporates the human insulin gene. By creating a colony of this modified bacteria, there can be rapid and cheap production of large quantities of human insulin. This can be used to treat type 1 diabetes.
• Disadvantages of GM crops:

  reduces biodiversity

  long term effects on human health

  if GM crops released into the natural environment they will create a 'Superweed' that is resistant to herbicides
• Clones are genetically identical individuals (copies), produced naturally by asexual reproduction. However, clones can also be made artificially.
• We can clone:

  Animals

  Plants
• Animals can be cloned using embryo transplants and adult cell cloning ( Dolly the Sheep).
• Plants can be cloned using cuttings or tissue culture.
• In adult cell cloning, an electric shock is applied (given) to the egg cell in order to stimulate (trigger) cell division
• Charles Darwin's theory of natural selection proposed that all species have evolved from simple life forms that first appeared on Earth more than three billion years ago
• Other theories of evolution proposed that changes in an organism over its lifetime could be passed on to its children. The most famous of these theories was Lamarck's theory of inheritance of acquired characteristics.
• Lamarck's theory about giraffes was that they have developed long necks over time from continual stretching to reach food.