B14 - Variation and evolution

• Variation


  Differences in the characteristics of individuals in a population
• No one else in the world will have exactly the same fingerprints as you
• Even identical twins have different fingerprints
• Nature - genetic variation


  The basic characteristics of every individual are the result of the genes they have inherited from their parents
• Nurture-environmental variation


  Some differences between you and other people are due entirely to the environment you live in
• Genetically identical plants can be grown under different conditions and will not look identical
• Plants deprived of light, carbon dioxide, or mineral ions do not make as much food and are smaller and weaker
• Many of the differences between individuals of the same species are the result of both their genes and the environment
• The only genetically identical humans are identical twins who come from the same fertilised egg
• Identical twins look and act in a remarkably similar way, but are never exactly identical as adults due to environmental effects
• Phenotype


  The physical characteristics of an organism
• Genes control the development of physical characteristics (phenotype), but the phenotype can also be changed by the environment
• Evolution by natural selection

  The theory that all species of living things have evolved from simple life forms that first developed over 3 billion years ago
• Mutations can introduce new variants into the genes of a species
• Survival of the fittest

  Individuals with characteristics most suited to the environment are more likely to survive to breed successfully
• Selective breeding


  The process of artificially selecting which members of a group to breed in order to get the characteristics of animals and plants that people want
• Selective breeding has resulted in plants and animals that are very different from their wild ancestors
• How selective breeding works

  1. Select animals/plants with desirable characteristics as breeding stock

  2. Breed them

  3. Select offspring with desired characteristics

  4. Repeat over many generations
• Examples of characteristics selected for in selective breeding

  • Disease resistance in food crops/garden plants
  • Animals that produce more meat or milk
  • Domestic animals with gentle nature
  • Large, unusual, brightly coloured or heavily scented flowers
• Selective breeding has resulted in animals and plants with strange combinations of genes that would probably never have occurred naturally
• Selective breeding has limitations as it can reduce genetic diversity
• den plants


  • animals that produce more meat or milk
  • domestic dogs and farm animals with a gentle nature
  • large, unusual, brightly coloured or heavily scented flowers
• The results of centuries of selective breeding have been dramatic. Our placid dairy cows that produce litres and litres of milk each day are very different to their aggressive wild ancestors that produced enough milk for their single calf and little more. Fields of wheat with their large and heavy heads of grain show little resemblance to the wild grasses that were their ancestors. Genetic manipulation by selective breeding has resulted in animals and plants with strange combinations of genes that would probably never have occurred naturally. However, organisms that are either useful or simply enjoyable have been produced as a result.
• Selective breeding


  • It greatly reduces the number of alleles in the population - because only individuals with the chosen alleles are allowed to breed
  • It reduces the variation between individuals
  • It reduces the variation in the alleles for a given characteristic
• When conditions are stable


  Reducing variation is not a problem
• When there is a problem - the climate changes or a new disease emerges


  The lack of variation can mean that none of the animals or plants in the population can cope with this change, resulting in the population dying out
• Bananas are all genetically very similar. The banana industry is at risk of being wiped out as a result of new aggressive diseases, because none of the plants are resistant to the pathogens.
• Some breeding populations have been so closely bred to achieve a particular appearance that animals are mated with close relatives. This results in very little variation in the population. Consequently, some breeds are particularly prone to certain diseases or inherited defects.
• Selective breeding


  A process where humans breed plants and animals for desired characteristics
• Desired characteristics


  • disease resistance
  • increased food production in animals and plants
  • domestic dogs with a gentle nature
  • heavily scented flowers
• Genetic engineering


  Modifying (changing) the genetic material of an organism by cutting out a gene for a desirable characteristic from one organism and transferring it to the genetic material in the cells of another organism
• Principles of genetic engineering

  1. Enzymes are used to isolate and 'cut out' the required gene from an organism

  2. The gene is then inserted into a vector using more enzymes

  3. The vector is then used to insert the gene into the required cells
• Genes are transferred to the cells at an early stage of their development (in animals, the egg, or very early embryo). As the organism grows, it develops with the new desired characteristics from the other organism. In plants, the desired genes are often inserted into meristem cells which are then used to produce identical clones of the genetically modified plant.
• Genetically engineered bacteria and fungi can be cultured on a large scale to make huge quantities of protein from other organisms, for example, human insulin and human growth hormone.
• Scientists have now found that genes can be transferred to animal and plant cells as well as bacteria and fungi. New techniques are making genetic modification of a wide range of organisms easier all the time.
• Crops that have had their genes modified by genetic engineering techniques are known as genetically modified crops (GM crops).
• Examples of genetically modified crops

  • Plants that are resistant to attack by insects because they have been modified to make their own pesticide
  • Plants that are more resistant than usual to herbicides
  • Plants that directly increase the size of the fruit or the nutritional value of the crop
• Increasing crop yields is extremely important in providing food security for the world's human population, which is growing all the time.
• Examples of genetically modified crops

  • Potatoes modified to make more starch and be more resistant to several common pests
  • Soybeans modified to produce a healthier balance of fatty acids
  • Rice plants modified to withstand being completely covered in water for up to three weeks and still produce a good crop
• Sometimes GM crops contain genes from a completely different species, such as the jellyfish genes added to crop plants. Sometimes genetic modification simply speeds up normal selective breeding, by taking a gene from a closely related plant and inserting it into the genome.