UNIT 4 INHERITANCE

• Selective Breeding


  Breeding the parents with the best characteristics, breeding their offspring with the best characteristics, repeating over many generations
• Genetic Engineering (genetic modification)


  Removing a useful gene from one species' DNA, making more copies of that gene by inserting them into a vector, inserting useful gene into the DNA of the species we want to change using enzymes
• Selective Breeding


  • Cows that have high milk yields or high quality meat; domestic animals with a good temperament; plants with good crop yields or attractive flowers
• Genetic Engineering


  • GM crops which have good yields, grow well in harsh conditions and are resistant to pesticides
• The GM species will immediately have the properties caused by the new gene
• Selective Breeding


  Reduces the gene pool, can lead to inbreeding which leads to health problems, is a very slow process (as it needs repeating over many generations)
• Genetic Engineering


  Technically difficult to do, is a new technology so long term effects are unknown, reduces the gene pool, genes from GM crops may spread to wild flowers which could affect the ecosystem
• Gamete


  A sex cell, containing half the number of chromosomes of a normal cell
• Chromosome


  Contains DNA
• Gene

  A small section of DNA, coding for a combination of amino acids, to make a specific protein
• Genome

  The entire genetic material of an organism
• Allele


  A different version of a gene
• Dominant allele


  Always expressed if there is at least one copy of it in the genotype
• Recessive allele


  Only expressed if there are 2 copies of it in the genotype
• Genotype


  The pair of alleles we have (e.g. Bb)
• Phenotype


  A physical characteristic we have (e.g. brown eyes)
• Homozygous


  The same alleles are present in the genotype (BB/bb)
• Heterozygous


  Different alleles are present in the genotype (Bb)
• GM crops


  Crops produced by genetic modification (genetic engineering)
• Variation occurs in offspring because when gametes fuse, their genetic information mixes
• DNA is a polymer, made up of 2 strands, forming a double helix shape
• In human cells there are 23 pairs of chromosomes (46 chromosomes in total) – one if each pair came from each parent
• The sex chromosomes are the 23rd pair: XX = female; XY = male
• All female gametes (eggs) contain an X chromosome; male gametes (sperm cells) can contain an X or a Y chromosome
• Variation is caused by the different genes that are inherited (e.g. eye colour), the environment (e.g. scars) and a combination of both (e.g. height)
• Genetic mutations are changes in our DNA, which alters the proteins that they code for. They happen when DNA copies itself during cell division and when the DNA exposed to ionising radiation.
• Evidence for evolution comes from studying fossils, as we can see how much or little different organisms have changed over time
• Evidence for evolution also comes from studying bacteria because they reproduce so quickly, so the evolution process is quicker
• Bacteria evolve to become resistance to antibiotics
• Traditionally, organisms were classified based on their structure and characteristics
• Organisms are now classified based on their internal structure, what their cells are like and their DNA as microscope technology has improved
• Organisms are given binomial names: First word = Genus (capital letter); second word = species (lower case) e.g. Panthera leo (lion)
• Natural Selection


  1. Random genetic mutations lead to variation within the species

  2. This gives some members a survival advantage

  3. They live long enough to breed

  4. They pass on their useful alleles to their offspring
• Speciation


  1. Two populations in a species become geographically isolated

  2. They evolve in different ways through natural selection

  3. Because their different environments bring different survival advantages

  4. They become so different that they cannot interbreed