Genetic Variation and Its Control

Genetic material
1. • A cell is the basic unit of life; all organisms are made up of cells.
2. • The nucleus is a large organelle found in all cells, that contains the genetic information.
3. • Chromosomes are thread-like structures made of DNA found in the nucleus
4. • Genes are small sections of a chromosome that control the characteristics of an organism.
5. • These are passed on from parent to offspring, resulting in offspring of plants and animals having similar characteristics to their parents. Eg hair colour and petal colour
Sexual reproduction
1. • Involves two parents.
2. • They produce male and female sex cells (gametes).
3. • In humans these are sperm and eggs.
4. • Fertilisation occurs - the joining (fusion) of male and female gametes.
5. • The mixture of the genetic information from two parents leads to variety in the offspring.
6. • Genes are passed on in the gametes, from which the offspring develop.
Asexual reproduction
1. • Involves only one individual as a parent.
2. • There is no fusion of gametes.
3. • There is no mixing of genetic information and so no variation in the offspring.
4. • These genetically identical individuals are known as clones.
5. Examples:
  1. • Bacteria or yeast cells use binary fission
    1. • Plants can use runners, bulbs or vegetative propagation.
      1. • Some invertebrate animals like starfish and hydra can produce asexual offspring.
Cloning
1. • Humans can carry out various procedures to create clones of plants and animals.
  1. • These new individuals are genetically identical to the parents.
    1. • New plants can be produced quickly and cheaply by taking cuttings from older plants.
2. Tissue culture
  1. • This uses small groups of cells from part of a plant to grow new plants.
3. Embryo transplants
  1. • This involves splitting apart cells from a developing animal embryo before they become specialised.
    1. • The identical embryos are then implanted into the wombs of host mothers
  2. Advantages:
    1. • This technique could be used to make many copies of cows that have a high milk yield.
    2. • It would produce a herd of cows much faster than if the original cow was used for breeding in the normal way.
  3. Concerns:
    1. • People do not want this procedure to be used in humans.
    2. • It could be used to provide more embryos for scientific testing.
Adult cell cloning
1. • The nucleus is removed from an unfertilized egg cell.
2. • This is replaced with the nucleus of an adult cell (eg skin cell).
3. • An electric shock is used to start the cell dividing to form embryo cells.
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 is inserted into the womb of an adult female to continue its development.
6. Advantages:
  1. • This could be used to clone animals with desired characteristics, eg farm animals.
  2. • It could possibly be used to save animals from extinction.
  3. Concerns:
    1. • People do not want human babies to be cloned.
    2. • If this is used in farming, it produces lots of genetically identical individuals;
    3. • If there is a change in the environment, they may all struggle to survive.
Genetic engineering
1. • Genes from the chromosomes of humans and other organisms can be cut out using enzymes and transferred to cells of other organisms.
  1. • Cut out the insulin gene from the DNA of a human cell using an enzyme.
    1. • Remove a ring of DNA from a bacterium and open it up using the same enzyme.
      1. • Insert the insulin gene into the plasmid using another enzyme.
        • Enable a bacterium to take up the altered DNA.
        • Put the bacterium in a fermenter, and it multiplies many times.
        • Each new bacterium contains the insulin gene.
        • The bacteria produce insulin which can be extracted.
2. Examples of uses in medicine:
  1. • Vaccine production
    1. • Production of insulin for diabetics.
3. Other uses of genetic engineering
  1. • Genes can also be transferred to the cells of animals or plants at an early stage in their development so that they develop with desired characteristics.
    1. • This could be used to insert ‘healthy’ genes into an embryo that has a genetic disease.
  2. • New genes can also be transferred to crop plants
    1. • Crops that have had their genes modified in this way are called genetically modified crops (GM crops).
      1. • Examples of genetically modified crops include ones that are resistant to insect attack or to herbicides.
        • GM crops generally show increased yields.
4. Concerns:
  1. • Long-term, unpredicted effects of consuming GM plants on human health.
    1. • People may want to manipulate the genes of their future children.
      1. Spreading to other plants

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Genetic Variation and Its Control

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