Inhertitance bio 2

• DNA


  The chemical that all of the genetic material in a cell is made up from
• DNA


  Contains coded information - the instructions to put an organism together and make it work
• DNA


  • Found in the nucleus of animal and plant cells, in really long structures called chromosomes
  • Normally comes in pairs
• DNA


  A polymer made up of strands coiled together in the shape of a double helix
• Genome

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


  • Allows scientists to identify genes linked to different diseases
  • Helps understand inherited diseases and develop treatments
  • Allows tracing the migration of human populations
• Sexual reproduction


  1. Fusion of male and female gametes

  2. Offspring contain a mixture of genetic information from both parents
• Asexual reproduction


  Only one parent, offspring are genetically identical clones
• Meiosis


  1. Cell division that produces gametes with half the normal number of chromosomes

  2. Chromosomes are shuffled and distributed randomly to the gametes
• X and Y chromosomes


  Control whether an organism is male (XY) or female (XX)
• Males have an X and a Y chromosome, females have two X chromosomes
• Genetic diagrams


  Show possible combinations of gametes and resulting offspring genotypes/phenotypes
• Alleles


  Different versions of a gene, can be dominant or recessive
• Most characteristics are controlled by multiple genes
• Characteristics controlled by single genes

  • Hair colour, red-green colour blindness
• All the offspring are normal (boring)
• Breeding two offspring from the previous cross

  1. Parents' phenotypes

  2. Parents' genotypes

  3. Gamete genotypes

  4. Offspring's genotypes

  5. Offspring's phenotypes
• Polydactyly is caused by a dominant allele
• Embryo screening during IVF


  1. Embryos are fertilized in a lab

  2. DNA is tested from each embryo

  3. Embryos with bad alleles would be destroyed
• Arguments against embryo screening

  • It implies people with genetic problems are 'undesirable'
  • There may be a point where everyone wants to screen for desirable traits
• Arguments for embryo screening

  • It will help stop people suffering
  • Treating disorders costs the government a lot of money
  • There are laws to stop it going too far
• Organisms of the same species have differences called genetic variation
• Genetic variation


  Differences between organisms of the same species
• Mutation


  A change to the sequence of bases in DNA
• Mutations can introduce variation
• If a new phenotype makes an organism more suited to the environment, it can become common through natural selection
• Theory of evolution by natural selection

  • Organisms show variation
  • Organisms compete for limited resources
  • Organisms with most suitable characteristics survive and reproduce
  • Characteristics that made them successful are passed to offspring
• New discoveries have helped develop the theory of evolution
• Speciation


  The development of a new species over a long period of time
• Extinction


  When no individuals of a species remain
• Reasons for extinction


  • Environment changes too quickly
  • Predator kills them all
  • New disease kills them all
  • Can't compete with another species for food
• Type


  Controlled by pines
• Over a long period of time, the phenotype of organisms can change so much because of natural selection that a completely new species is formed
• Dodos are now extinct because humans not only hunted them, introduced other animals which ate all their eggs, and we destroyed the forest where they lived - they really didn't stand a chance
• Natural selection is all about the organisms with the best characteristics surviving
• Selective breeding


  Taking the plants or animals with the desired characteristics and breeding them together to get the best possible offspring
• Selective breeding process


  1. Select the plants/animals with the desired characteristics

  2. Breed them together

  3. Select the offspring with the desired characteristics and breed them together

  4. Continue this process over generations until the desired trait is established in all the offspring
• Selective breeding can be used to improve yields in farming, e.g. breeding cows and bulls with the best characteristics for producing meat to get cows with a very high meat yield
• Drawbacks of selective breeding

  • Reduction in the gene pool (number of alleles/forms of a gene) due to inbreeding
  • Increased chance of inheriting harmful genetic defects
  • Less genetic diversity makes the population more vulnerable to new diseases
• Antibiotic resistance is becoming more common, partly because of the overuse and inappropriate use of antibiotics