B1.7 Genetic Variation

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B1.7.1 Reasons for variation

Genes work at the molecular level to produce characteristics. A plant or animal recieves half its genes from its mother and half from its father during fertilisation, so has similar characteristics but is not identical to its parents.

The nucleus of a cell has chromosomes, which carries genetic information. Different genes control the development of different characteristics of an organism.

Genetic variation/causes- Differences in characteristics caused by differences in genes inherited

  • Eye colour
  • Gender

Environmental variation/causes- Differences in characteristics caused by differences in conditions in which developed

  • Riding bike -> scars
  • Training -> strength

Combination of both causes- Most variations caused by both

  • Weight
  • Skin colour
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B1.7.2 Reproduction

Sexual reproduction 

  1. Gamete from mother fuses with gamete from father to form zygote
  2. Genetic information from each parent mixes
  3. Genetic variation is natural: offspring have different combinations of genes, so show variety in characteristics

Asexual reproduction

  1. No fusion of gametes, only an individual needed to be a parent
  2. No mixing of genetic information
  3. No genetic variationin offspring: all offspring genetically identical, so are clones.
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B1.7.2 Cloning

Plants

Plant cuttings- quick and cheap

  1. Several cuttings taken from parent plant
  2. Stem planted and auxins used to encourage roots to grow
  3. Cuttings grown into new plants that are genetically identical

Tissue culture- expensive and difficult

  1. Tissue sample scraped from the parent plant and separated into different cells
  2. Samples placed in agar growth medium with nitrients and auxins
  3. Samples develop into tiny plantlets
  4. Planted into compost. Hormones make the cells divide rapidly, then differentiate into stem, root and leaf cells

Animals

Embryo trasplantation- best way ro clone small numbers of animals at the same time

  1. Splitting developing embryos- separating cells
  2. Grown into embryos in a lab
  3. Transplanted into the uterus of a host/surrogate mother
  4. Offspring genetically identical/clones of each other
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B1.7.2. Cloning cont.

Adult cell cloning- 

  1. Nucleus removed from an unfertilised egg cell (enucleated)
  2. Diploid nucleus from another animal's body cell (e.g. skin cell) is inserted into the enucleated egg cell
  3. Fused cell given a mild electric shock to stimulate division and form embryo
  4. Implanted into uterus of adult female to develop intil birth
  5. Offspring genetically identical to the animal of which the adult skin cell was extracted

Ethics in cloning

  • High mortality rate
  • Unnatural
  • Underdeveloped organs
  • Religious issues (playing god)
  • Unrealistic expectations of offspring
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Cloning diagram

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B1.7.2 Genetic Engineering

Genetic engineering is the transfer of a gene frome one organism to another so tat the desired characterisitc is produced in that organism

  1. Find gene with specific characteristic wanted
  2. Cut out of this gene using enzymes
  3. Insert into the chromosome of an embryo in a different organism
  4. Empryo implanted into womb

Uses

  • Bacteria genetically modified to produce insulin
  • GM crops genetically modified to resist attack by insects or to herbicides, to increase yield

Issues with new science

  • Economic- is it worth the cost?
  • Social- Are the benefits for people/society greater than the problems?
  • Ethical- Is it right/wrong/fair to do this?

Issues with GM crops

  • Herbicide resistant -> gene transferred to weeds -> herbicide no longer kills weeds
  • Herbicide resistant -> clears weeds -> less food for insects -> less food for insect eaters
  • Insecticide resistant -> pest insects develop resistance to chemical made by gene
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