genetics and evolution

• how bacteria become resistant:

  • a mutation occurs that makes the bacterium resistant to an antibiotic
  • initially the mutation has no real advantage
  • if the antibiotic is used, the non-resistant bacteria die and the resistant bacteria have the advantage to survive
  • the antibiotic resistant bacteria reproduce and pass the resistance to their offspring becoming the dominant species
• how does selective breeding work?

  1. select female that shows the feature you are looking for (be specific and use the exam question)
  2. select male with best desirable feature
  3. breed the best female with the best male
  4. select offspring that show the specific trait
  5. continue breeding and select BEST offspring from each generation
  6. repeat for several generations
• selective breeding is the process by which humans use animal and plant breeding to selectively develop particular phenotypic traits
• benefits of selective breeding:

  • humans can manipulate organisms to benefit them
  • new variations of organisms can be produces (e.g cabbage, broccoli, cauliflower are all variations of the same plant)
• limitations to selective breeding:

  • selectively bred organisms are more susceptible to environmental changes and diseases
  • inbreeding can become a problem
  • in animals artificial selection can cause health problems
• genetic engineering - a process which involved modifying the genome of an organism, by introducing a gene from another organism, to give a desired characteristic
• plasmid - a ring of dna that acts as a vector
• modified crops which produce their own pesticides: kill pests, increase yield and profit

  crops which are resistant to herbicides: spray herbicide - kill weeds, increase yield and profit

  crops that produce higher yields: profit
• advantages of GMO:

  • herbicides will kill weeds but not crop
  • higher yields of crop
  • increased profits
• disadvantages of gmo:

  • reduced genetic variability in ecosystem
  • other species of plants may become resistant to herbicide
  • possible devastating effect on future crop growth
  • effects on ecosystem on spread of herbicide resistant plants
• clone - a group of genetically identical cells or organisms
• uses of clones in plants and animals:

  • stem cells - medical/scientific research
  • asexual reproduction of plants - such as growing potatoes or daffodils
  • reproductive cloning - make copies of a high value animal
• What is the first step in the tissue culture process for carrots?

  The carrot is washed in disinfectant
• Why is the carrot washed in disinfectant?

  To remove harmful microbes
• What tool is used to chop the carrot root into discs?

  A sterile knife
• What are the root discs pressed onto?

  A dish containing agar jelly
• What is included in the agar jelly for the carrot tissue culture?

  Food and growth hormones
• What conditions are maintained in the incubator for the tissue culture?

  Constant warm temperature and light
• What develops from the mass of cells in the tissue culture?

  A callus
• What happens to the callus after it develops?

  It is transferred to a new agar dish
• What does the new agar dish contain for the callus?

  Hormones and nutrients
• How long is the callus left in the incubator?

  Several weeks
• What develops from the callus after several weeks?

  Tiny carrot plants with roots and leaves
• Where are the tiny carrot plants transferred after development?

  To a flask with more nutrients
• What happens once the plantlets grow into small plants?

  They can be planted into soil
• advantages to the gardener of producing geraniums from cuttings rather than from seeds:

  • quicker to grow a plant from a cutting than from a seed
  • cuttings produce clones plants identical (to parents) / outcome unknown
• cuttings - taking small pieces of a stem or leaf and growing it in the right conditions to produce a new plant
• tissue culture - getting a few cells from a desirable plant to make a big cell mass of identical cells each of which can produce a tiny identical plant
• asexual reproduction - reproduction which involves only one parent, there is no joining of gametes and the offspring are genetically identical to the parent
• embryo cloning - splitting apart cells from a developing embryo before they become specialised to produce several identical embryos
• tissue culture:

  1. a small amount of parent tissue or a number of cells is taken and the surface sterilised
  2. the tissue is transferred to a sterile nutrient jelly called agar
  3. auxins (growth hormones) are added to stimulate the cells to divide by mitosis
  4. cells grow rapidly into small masses of tissue (called a callus)
  5. more growth hormones (a different combination) are now added to stimulate the growth of roots and stems
  6. the tiny platelets are transferred into potting trays where they develop into plants
• embryo cloning:

  1. sperm is taken from the best bull and used to fertilise an egg from the best cow
  2. the fertilised egg divides to form an embryo containing several cells
  3. the embryo is separated into individual cells, which go on to form new embryos. each embryo contains the same genes
  4. the embryos are implanted into surrogate cows
  5. the cows give birth to calves, which are all clones of each other
• adult cell cloning:

  1. the nucleus is removed from an unfertilised egg cell
  2. the nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell
  3. an electric shock stimulates the egg cell to divide to form an embryo
  4. these embryo cells contain the same genetic information as the adult skin cell
  5. when the embryo has developed into a ball of cells it's inserted into the womb of an adult female to continue its development
• advantages of adult cell cloning:

  • genetically identical offspring are guaranteed to inherit the desirable characteristics you want them to have e.g high milk/meat yield; disease resistance; colour; taste; etc
  • clone useful GMOs
  • cloning to save animals from extinction
  • potential to clone human tissue for transplants
• disadvantages of adult cell cloning:

  • lack of genetic variation = small gene pool;
  • can mean that whole population is wiped out if conditions chnage - e.g by a disease
  • only useful if you already have something with good characteristics to clone
  • bad features inherited by clones too
  • hard to clone animals
  • ethical issues - eg with using embryos + "designer babies" / cloned pets
• mendel using plants instead of animals is good because they're easy to take care of, cheap, grow quick and it's easy to control breeding through cross pollination
• In the mid-19th Century Gregor Mendel carried out breeding experiments on plants. One of his observations was that the inheritance of each characteristic is determined by ‘units’ that are passed on to descendants unchanged.

  In the late 19th Century behaviour of chromosomes during cell division was observed.
• In the early 20th Century it was observed that chromosomes and Mendel’s ‘units’ behaved in similar ways. This led to the idea that the ‘units’, now called genes, were located on chromosomes.

  In the mid-20th Century the structure of DNA was determined and the mechanism of gene function worked out.

  This scientific work by many scientists led to the gene theory being developed.
• a child saved seeds from an apple and planted them. the new apples didn't taste like the original ones. why?

  • seeds are produced by sexual reproduction/fusion of gametes
  • so get a mixture of genes/genetic information/chromosomes/DNA
• advantages of using tissue culture:

  • you can produce large amounts of plants from a small piece of tissue
  • plants are clones of original tissue so will be guaranteed to have the same features