Topic 6 - Inheritance, Variation and Evolution

• DNA is the chemical that carries the genetic information of an organism.
• DNA contains coded information which is the instructions to put an organism together and make it all work
• Chromosomes normally come in pairs
• DNA is a polymer, it is made of two strands coiled together in the shape of a double helix
• A gene is a small section of DNA found on a chromosomes
• Each gene codes for a particular sequences of amino acids which are put together to make a specific protein
• Every organism has a genome
• Genome is the entire set of genetic material in an organism
• Importance understanding of human genome:

  • identify genes linked to different diseases
  • this can help develop effective treatment
  • can be used to trace migration of certain populations around the world
• DNA is made up of nucleotides
• Nucleotides are polymers made up of lots of repeating units
• Each nucleotide consist of a sugar, a phosphate and a base
• The sugar and phosphate groups alternate. One of four different bases (A, T, C or G) joins each sugar
• Enzymes act as biological catalysts to speed up chemical reactions in the body
• Structural proteins are physically strong
• Collagen is a structural protein that strengthens connective tissue (like ligaments and cartilage )
• Hormones are used to carry messages around the body
• Insulin is a hormone released into the blood by the pancreas to regulate the blood sugar levels
• mRNA acts as a messenger between the DNA and the ribosome
• mRNA carries the code to the ribosomes
• Proteins are made in the cell cytoplasm on tiny structures called ribosomes
• A mutation is a random change in an organisms DNA. They sometimes can be inherited.
• There are different types of mutation:

  • insertions
  • deletions
  • substitutions
• Insertions are where a new base is inserted into the DNA base sequences where it shouldn’t be
• An insertion changes the way the groups of the three bases are read, which can change the amino acids that they code for
• Insertions can change more than one amino acid as they have a knock-on effect on the bases further on in the sequence
• Deletions are when a random base is deleted from the dna base sequence
• Like insertions, deletions change the way that the base sequence is read and have knock on effects further down the sequence
• Substitution mutations are when a random base in the DNA base sequence is changed to a different base
• Most mutations have very little or no effect on the protein. Some will change it to such a small extent that it’s function or appearance is unaffected
• Mutations change the sequence of the DNA bases in a gene, which produces a genetic varient
• Sexual reproduction is where genetic information from two organisms is combined to produce offspring which are genetically different to either parent
• Sexual reproduction involves the fusion of male and female gametes
• In asexual reproduction there’s only one parent. There’s no fusion of gametes, no mixing of chromosomes and no genetic variation between parent and offspring. The offspring are genetically identical to the parent - clones
• In humans, each gamete contains 23 chromosomes
• The mother and father produce gametes by meiosis
• Asexual reproduction advantages:

  • only one parent
  • use less energy as they don’t need to find a mate
  • faster
  • many identical offspring in favourable conditions
• The classification system was created by Carl Linnaeus in the 18th century
• Living organisms are classified into groups by their structure
• The classification system includes 5 kingdom:

  • animals
  • plants
  • fungi
  • prokaryotes
  • protists