variation

• What is variation?

  Differences in the characteristics of individuals in a population
• Three causes of variation in any population?

  • the genes/alleles they have inherited (genetic causes)
  • the conditions in which they have developed (environmental causes)
  • a combination of genes and the environment
• Why does genetic variation occur?

  mutations
• What are mutations?

  random changes to DNA
• When do mutations take place?

  all the time
• mutations and the phenotypes?

  most have no effect on the phenotype; some influence phenotype; very few determine phenotype.
• When can new phenotypes due to mutations (which is rare) be beneficial?

  if the environment changes (e.g. a new virus)
• When do scientists believe life first developed on earth?

  more than 3 billion years ago
• What does the theory of evolution by natural selection state?

  The theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago.
• how does evolution work (example answer)?

  • .... with more beneficial alleles for ..... (depending on the change) is more likely to successfully survive and reproduce
  • these alleles are passed down to their offspring
  • over many generations alleles for ..... will be widespread in the population
• define evolution?

  the change in the inherited characteristics of a population over time through a process of natural selection
• What happens when two populations of one species become very different in phenotype?

  they can't interbreed to produce fertile offspring so they're two different species
• How long has selective breeding been used?

  for thousands of years since they first bred food crops from wild plants and domesticated animals
• what is selective breeding?

  Selective breeding (artificial selection) is the process by which humans breed plants and animals for particular genetic characteristics.
• Selective breeding step by step?

  1. choosing parents with the desired characteristic from a mixed population
  2. they are bred together
  3. from the offspring those with the desired characteristic are bred together
  4. this continues over many generations until all the offspring show the desired characteristic
• disadvantage of selective breeding?

  Selective breeding can lead to ‘inbreeding’ where some breeds are particularly prone to disease or inherited defects.
• What are genes?

  sections of DNA on a chromosome
• What does each gene code for?

  the amino acid sequence of a specific protein
• What happens in genetic engineering?

  genes from one organism (e.g. humans) are cut out and transferred to cells of a different organism (e.g. bacteria) so the genome of the bacteria is modified and includes a human gene
• What is insulin?

  a hormone involved with blood glucose regulation in humans
• How does genetic engineering work for type 1 diabetes?

  they can't produce their own insulin so bacteria is genetically modified to contain the human insulin gene so the bacteria can produce human insulin which can be purified and used for type 1 diabetes
• What are GM crops?

  genetically modified crops as genes have been transferred into them
• What do GM crops show?

  a greater yield than normal crops
• examples of GM crops?

  GM crops include ones that are resistant to insect attack or to herbicides.
• concerns about GM crops?

  • the effect on populations of wild flowers and insects could be harmful (GM crops could be unsafe)
  • the effects of eating GM crops on human health have not been fully explored
• What is gene therapy?

  genetic modification is currently being explored as a way to treat inherited disorders in humans
• Issues with gene therapy?

  long-term effects are unknown (e.g. if we modify a gene the effect on other genes is unknown)
• genetic engineering step by step?

  • enzymes are used to isolate the required gene
  • this gene is inserted into a vector (usually a bacterial plasmid or a virus)
  • the vector is used to insert the gene into the required cells
  • genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics
• Why are genes transferred at an early stage in genetic engineering?

  genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics
• advantage of cloning plants?

  the clone is genetically identical to the original plant so you already know that its characteristics will be
• What is cuttings in plant cloning?

  a method that has been used for a long time by scientists
• What happens in plant cloning using cuttings?

  • a small piece of the plant is removed and the end is dipped in rooting powder (contains plant hormones which encourages the plant to develop roots)
• when are cuttings useful?

  if you only want a few clones of the original plant
• What is used when hundred of clones of a plant are needed?

  tissue-culture
• tissue culture (plant cloning) step by step?

  • take the plant we want to clone and divide it into hundreds of tiny pieces (each piece contains a small number of cells)
  • incubate these small groups of cells with plant hormones
  • the plant hormones stimulate the plant to grow and develop into fully grown clones
• how must conditions be for a tissue-culture (cloning plants)?

  completely sterile as we don't want to introduce any microorganisms such as bacteria or fungi
• Where is tissue-culture extremely useful and why?

  commercial plant nurseries as it allows growers to produce thousands of genetically identical plants quickly and cheaply
• How can tissue cultures be used (rare plants)?

  to preserve rare species of plants
• animal cloning using embryo transplants (sperm and egg cell)?

  sperm and egg cell -> fertilisation produces a fertilised egg -> allow the fertilised egg to develop into an early stage embryo (with none of its cells beginning to specialise) -> split the embryo in half using a glass rod -> transplant into two host mothers -> two identical offspring produced
• issue with embryo cloning?

  we start with sperm and egg cell so can't be sure the offspring will have the characteristics we want