Biology inheritance

• Selective Breeding


  Breeding the best plants or animals together to get the best possible offspring
• Selective Breeding


  1. Select the ones with the desired characteristics

  2. Breed them together

  3. Select the best offspring

  4. Repeat over several generations
• Selective Breeding used in agriculture


  • Breeding cows and bulls with best characteristics for high meat yield
• Selective breeding is not new, it's how we got edible crops from wild plants and domesticated animals
• Reduction in gene pool


  • Fewer different alleles (forms of a gene) in the population
  • Increased chance of inheriting harmful genetic defects due to inbreeding
  • Increased susceptibility to new diseases
• Selective breeding reduces the number of different alleles (forms of a gene) in the population
• Inbreeding can cause health problems due to increased chance of inheriting harmful genetic defects
• Reduced gene pool makes populations more susceptible to new diseases
• Meiosis


  The formation of four non-identical cells from one cell
• Mitosis


  The formation of two identical cells from one cell
• Sexual reproduction


  1. Joining of male and female gametes, each containing genetic information from the mother or father

  2. Sperm and egg cells in animals

  3. Pollen and egg cells in flowering plants
• Gametes are formed by meiosis, as they are non identical
• Normal cell


  Has 46 chromosomes, two sets of 23 chromosomes (one from each parent)
• Gamete


  Has 23 chromosomes, fuses in fertilisation
• The genetic information from each parent is mixed, producing variation in the offspring
• Asexual reproduction


  1. One parent with no gametes joining

  2. Happens using the process of mitosis, where two identical cells are formed from one cell

  3. No mixing of genetic information

  4. Leads to clones, which are genetically identical to each other and the parent
• Organisms that reproduce asexually

  • Bacteria
  • Some plants
  • Some animals
• Meiosis


  1. Cell makes copies of its chromosomes

  2. Cell divides into two cells, each with half the amount of chromosomes

  3. Cell divides again producing four cells, each with a quarter the amount of chromosomes

  4. These cells are called gametes and they are all genetically different from each other
• Gametes with 23 chromosomes join at fertilisation to produce a cell with 46 chromosomes, the normal number
• This cell divides by mitosis to produce many copies, and an embryo forms
• The cells begin to take on different roles after this stage (differentiation)
• Advantages of sexual reproduction

  • Produces variation in offspring
  • Allows selective breeding
• Advantages of asexual reproduction

  • Only one parent is needed
  • Uses less energy and is faster as organisms do not need to find a mate
  • In favorable conditions lots of identical offspring can be produced
• Organisms that use both sexual and asexual reproduction

  • Malarial parasites
  • Some fungi
  • Some plants
• DNA


  The genetic material in the nucleus of a cell, composed of a chemical called DNA
• Gene


  A small section of DNA on a chromosome that codes for a specific protein
• Genome


  All the genes coding for all of the proteins within an organism
• The whole human genome has now been studied and this has improved our understanding of the genes linked to different types of disease, the treatment of inherited disorders and has helped in tracing human migration patterns from the past
• DNA


  A polymer made up of two strands which wrap around each other like a rope in a double helix structure
• Nucleotide


  The small parts that DNA is made up of, consisting of one sugar molecule, one phosphate molecule and one of four organic bases (A, C, G, T)
• Complementary base pairing


  A bases only connect to T bases, and C bases only connect to G bases
• Protein synthesis


  The process of producing a protein from DNA
• Protein synthesis


  1. DNA contains the genetic code for making a protein

  2. The two DNA strands pull apart and mRNA nucleotides match to their complementary base on the strand

  3. The mRNA strand is created as a template of the original DNA

  4. The mRNA moves to the ribosomes where the bases are read in threes to code for an amino acid

  5. The corresponding amino acids are brought to the ribosomes and connected together to form a protein

  6. The protein folds to form a unique 3D structure
• Protein


  Can be enzymes, hormones or structural proteins
• Mutation


  A change in the sequence of bases in DNA, either an insertion, deletion or substitution
• Most mutations do not alter the protein or only do so slightly, but some can have a serious effect and change the shape of the protein
• Variation between organisms arises from the coding DNA that determines the proteins and their activity, and the non-coding DNA that determines which genes are expressed
• Gamete


  An organism's reproductive cell (egg in female and sperm in males), which has half the number of chromosomes (23)
• Chromosome


  A structure found in the nucleus which is made up of a long strand of DNA
• Gene


  A short section of DNA that codes for a protein, and therefore contribute to a characteristic