Evolution

• A mutation occurs when DNA is permanently changed which can alter the genetic message carried by that gene. This can be shown throughout a family and can be passed down through generations. Mutations add a new alleles to a gene pool.
• A mutant is resulting from or showing the effect of a mutation
• Mutations can occur in somatic cells or germline cells.
• Mutations in somatic cells are in a single body cell and the individual will be affected. it cannot be inherited so once the individual dies, the mutation is lost. For example, cancerous growths
• Mutations in germline cells occur in gametes and can be passed onto offspring (every cell in the entire organism of the offspring will be affected) but it is most likely that the actual individual won't be affected. For example, Phenylketonuria (PKU)
• Gene mutations or point mutations is when a single gene is changed or destroyed during DNA replication before cell division or by a mutagen. This is when that matching of complimentary bases don't happen or match and can be lethal
• Types of point mutation:

  • substitution
  • frameshift
  • insertion
  • deletion
• Substitution point mutation is when an existing nucleotide is replaced with another one with a different base
• Frameshift point mutation is when bases or nucleotides are added or removed to or from the strand resulting in new codons coding for different amino acids

  • insertion - new nucleotide added
  • deletion - a nucleotide is removed
• Duchenne Muscular Dystrophy is a genetic disorder (mutation) carried on the X chromosome causing progressive muscle weakness. This is caused by the alterations of a protein called dystrophin that keeps muscle cells in tact. It has no cure but the focus is on treating and managing symptoms to slow progression.
• Cystic fibrosis is a progressive genetic disease from a mutation on chromosome 7. It causes persistent lung infections and limits the ability to breathe over time. Its inheritance is autosomal recessive
• Chromosomal mutations are changes in which all or part of a chromosome is affected, occurring during crossing over in meiosis.
• Types of chromosomal mutations are:

  • duplication (or insertion) - a sections of a chromosome occurs twice
  • deletion - a piece of DNA is removed
  • inversion - breaks occur in the chromosome and the broken piece joins back to the DNA strand the wrong way around
  • translocation - part of the chromosome breaks off and is rejoined to the wrong chromosome
  • non-disjunction - homologous chromosomes do not separate so one daughter cell has an extra chromosome and one has one less
• Examples of chromosomal mutations:

  • trisomy
  • down syndrome - extra chromosome 21
  • Klinefelter's syndrome - male inherits extra X chromosome
  • monosomy
  • Cri-du chat syndrome - missing a portion of chromosome 5
  • Turner's syndrome - female missing an X chromosome
• lethal recessive is a recessive allele that when inherited in the homozygous condition results in the death of an embryo, foetus, or child e.g. Tay-sachs disease
• causes of mutation:

  • errors in DNA replication
  • somatic or germline
  • deletion, insertion, or duplication of DNA
  • e.g. cystic fibrosis, Huntington's disease, Tay-sachs
  • errors in cell replication
  • non-disjunction
  • germline cells
  • e.g. Turners or Klinefelter's syndrome, down syndrome
  • mutagens
  • an agent or substance that can bring about a mutation
  • e.g. mustard gas, sulphur dioxide, some antibiotics
• Mutagens can do the following:

  • trigger DNA replication errors
  • cause DNA breakages or lengthening
  • block DNA replication
  • chemically react to modify the DNA
  • cells that may be damaged can multiply
• Mutagens:

  • affect one gene or whole chromosome
  • occurs in somatic or germline cells
  • can affect the individual
• evolution


  the slow process of change in characteristics over time
• species


  a group of organisms which can interbreed to produce fertile offspring
• population


  a group of the same species that can often be further broken down into gene pools
• gene pool


  all the genes within a population, containing a variety of alleles which are constantly changing
• factors that influence allele frequencies

  • mutations
  • natural selection
  • random genetic drift
  • migration
  • barriers to gene flow
  • genetic diseases
• natural selection

  • survival of the fittest
  • individuals with more heritable traits are more likely to survive and reproduce and so will pass those favourable traits onto the next generation meaning less favourable characteristics will not be passed on
  • this is not by chance
• Factors of natural selection

  • Variation
  • Struggle for existence
  • Overproduction
  • Survival of the fittest
  • Like produces like
  • Over time
• Variation


  Individuals are not all the same due to differences in their genes, some of which may give selective advantage
• Struggle for existence


  Excessive birth rates and limited resources causes a struggle between individuals
• Overproduction


  Populations don't increase quickly in size because individuals must compete for limited supply and constantly adapt to the changing environment
• Survival of the fittest

  Only the best adapted individuals survive to reach maturity and reproduce due to their selective advantage
• Like produces like


  Favourable characteristics are passed onto the next generation
• Over time


  Proportion of less favourable alleles increases as less favourable alleles decreases
• random genetic drift is the change in alleles frequency in a population due to a result of chance events, mainly in small populations. This is by two mechanisms:

  • founder effect
  • bottleneck effect
• founder effect

  • small, isolated population moves and splits itself away from the main population
  • by chance as breeding is not equal among the population
  • forms a new community
  • new colony started by members of the original population
  • small population means new colony may have
  • reduced genetic variation
  • non-random sample of genes in the original population
• The Dunkers is an example of the founder effect

  • religious population originating in Germany migrated to America
  • nearly 60% had blood type A
  • USA had 40% blood type A
  • they do not permit to marry outside their group so they are an isolated population within USA
• Ashkenazi Jews is an example of the founder effect

  • originated in a small community in central and eastern europe
  • geographically isolated and only marry within their group
  • Tay-Sachs is prevalent
• bottleneck effect

  • natural disaster causes a portion of the population to be randomly eliminated
  • those who survive may have a different frequency of alleles in the gene pool from the original population
  • could result in a change of phenotype which will reflect the genetics of the surviving population
• Micronesian Island of Pingelap is an example of bottleneck effect

  • typhoon killed 90% of population
  • 20 survivors
  • one survivor has achromatopsia causing colour blindness and extreme light sensitivity
  • passed on and increased allele frequency
• Migration is when gene flow occurs, meaning individuals of a population move to a new location. This causes gene flow and new individuals may introduce new alleles or increase the frequency of other alleles within the gene pool.
• The increase of - blood type is an example of migration

  • the Chinese population all had Rh+ blood
  • Chinese traded with Europe and Europeans introduced the Rh- blood type
  • the frequency of this blood type is still considered low
• The increase of antigen 1B in Europe and Asia is an example of migration

  • Mongols have higher proportion of this allele
  • Mongols invaded Europe causing an increase in this allele in Asia and Europe