B6- Inheritance, variation and evoloution

• what does DNA stand for?

  Deoxyribonucleic acid
• what are chromosomes?


  Thread-like structures made of DNA and proteins that carry genetic information.
• what do coiled DNA strands make?

  double helix shape
• what is a gene?


  a small section of DNA found on a chromosome
• what does each gene code for?

  a particular sequence of amino acids which are put together to make a specific protien
• how many amino acids are used?

  20
• meiosis leads to non-identical cells being formed while mitosis leads to identical cells being formed.
• Sexual reproduction


  Fusion of male and female gametes. There is a mixing of genetic information which leads to variety in the offspring
• Asexual reproduction


  Involves only one parent and there is no fusion of gametes. There is no mixing of genetic information and it leads to genetically identical offspring (clones)
• Meiosis


  The type of cell division that produces gametes
• Cell division by meiosis

  1. The genetic material is replicated

  2. The cell divides twice to form 4 gametes, each with a single set of chromosomes

  3. All gametes are genetically different from each other
• DNA


  Double helix
• Gene


  A small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids to make a particular protein
• Genome


  The entire genetic material of an organism
• Understanding the human genome

  • Searching for genes linked to different types of disease
  • Understanding and treatment of inherited disorders
  • Tracing human migration patterns from the past
• Allele


  Version of a gene
• Dominant


  Only 1 copy of the allele is needed to display the characteristic
• Recessive


  2 copies of the allele are needed to display the characteristic
• Homozygous


  2 identical copies of an allele
• Heterozygous


  2 different copies of an allele
• Genotype


  The combination of alleles
• Phenotype


  The physical characteristics of an organism
• Polydactyly is caused by a dominant allele
• Cystic fibrosis is caused by a recessive allele
• The genotype of a female is XX
• The genotype of a male is XY
• Variation


  The difference in characteristics of individuals in a population
• Mutation


  A change in the DNA which could lead to a new phenotype
• Evolution


  A change in the inherited characteristics of a population over time through a process of natural selection. It may result in the formation of a new species
• Species


  Organisms that can interbreed to produce fertile offspring
• Selective breeding


  Process by which humans breed animals and plants for particular genetic characteristics. This continues over many generations until all the offspring show the desired characteristics
• Genetic engineering


  A process which involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic
• Genetically engineered bacterial cell


  • Bacteria that can produce insulin
• Genetic engineering


  1. Enzymes are used to cut out the required gene

  2. The gene is inserted into a vector (a bacterial plasmid or a virus)

  3. The vector is used to insert the gene into the required cells

  4. These genes should be transferred to the cells of animals, plants or microorganisms at an early stage of their development so they develop with the desired characteristics
• Evidence for evolution


  • Fossils
  • Antibiotic resistant bacteria
• Fossils


  The 'remains' of organisms from millions of years ago which are found in rocks
• Ways that fossils can be formed

  1. Parts of the organism have not decayed as the conditions for decay are absent e.g. it is too cold (trapped in ice), lack of oxygen (trapped in amber)

  2. Hard parts are replaced by minerals as they decay

  3. Preserved traces of organisms such as footprints, burrows and rootlet traces
• The fossil record is incomplete because: 1)Destroyed by geological activity 2) Many fossils have not been discovered 3) Many early organisms were soft bodied and had no hard parts 4) The correct conditions to form fossils are not present e.g. too hot
• Extinction


  There are no remaining individuals of a species left alive
• Causes of extinction


  • Destruction of habitat
  • New predator
  • New disease
  • Catastrophic event e.g. volcanic eruption