C7

• GENE POOL

  • Complete set of alleles in a population
  • Population = an interbreeding group pf organisms of the same species living in the same region at the same time.
  • Allele (variations of a gene) frequency = proportion of an allele from all alleles in the population.
• • Homozygous dominant (AA) 
  • Homozygous recessive (aa) 
  • Heterozygous (Aa) 
• FACTORS THAT EFFCT ALLELE FREQUENCY

  1. Mutations 
  2. Genetic drift 
  3. Gene flow 
  4. Natural selection (environmental selection pressures) 
  5. Non-random mating
• Genotype 

  • Different combination of alleles 
• Phenotype 

  • Observable physical trait 
  • Made by a genotype + environment 
• SELECTION PRESSURES

  • Abiotic or biotic factors of the environment that gives organisms with certain phenotype and advantage over others.
  • These organisms are able to survive and reproduced to pass alleles to offspring.
• 3 types of selection pressures: physical, biological and chemical.
• NATURAL SELECTION

  • Occurs when allele frequencies of a gene pool change due to environmental selection pressures that create selective advantage for certain phenotypes.
  • Decreases the genetic diversity of a population.
  • A process that occurs when a particular environment causes some organisms with a particular heritable trait (phenotype) that is considered advantageous.
  • This increases survival and reproduction compared to those without it.
  • Selection pressures determine survival of an organism and change of allele frequency.
• GENETIC DRIFT

  • A change in allele frequency of a population due to chance 
  • Genetic drift decrease the genetic diversity of a population
  • Allele frequency decreases
  • Reduction in population size (random event/migration) 
  • Reduction in variation

  
• BOTTLENECK EFFECT

  • Population reduced by a random event (natural disaster etc.) 
  • The size of a population is severely reduced for at least one generation 
  • Survivor's allele frequencies are unrepresentative of original population  
  • Decrease in genetic diversity and Change in allele frequency of population 

  
• FOUNDERS EFFECT

  • Small group of random individuals of a larger population moves and establishes colony in new location 
  • Selection pressures on founder population is different due to new environment (allopatric speciation) 
  • Decrease in genetic diversity and change in allele frequency 

  
• GENE FLOW

  • The movement of alleles between populations by interbreeding 
  •  Gene flow increases genetic diversity in a population.
  • Allele frequences decreases
  • Individuals enter gene pool (immigration) -> adding alleles 
  • Individuals leaving gene pool (emigration) -> removing alleles 
  • Migrant group is non-representative of original population

   
• • Immigration of individuals and interbreeding occurs -> new alleles added to gene pool -> increase genetic diversity
  • Emigration of individuals -> existing alleles are removed from gene pool -> decrease genetic diversity 

   

  
• Natural selection and genetic drift decrease the genetic diversity of a population but gene flow increases genetic diversity in a population.
• MUTATIONS

  • Random changes in DNA sequence
  • Responsible for introducing new alleles into a population --> increase genetic diversity.
  • Can happen spontaneously or as a result of mutagens (factors that cause mutations - physical/chemical)
  • Mutations can occur at several different levels – DNA, RNA or chromosomal.
• POINT MUTATIONS (Small)

  • One nucleotide base is affected.

  A) Ways one nucleotide base can be effected

  
• Silent mutations (substitution) 

  • One base pair changed, but codes for same amino acid.  
  • The genetic code is degenerate, keeps chain length
•  

  Missense mutations (substitution) 

  • One base pair changes and codes for different amino acid.  
  • Changes one amino acid in sequence, keeps chain length 
• Nonsense mutations (substitution) 

  • One base pair changes and codes for a premature STOP codon 
  • Produces shortened chain 
•  

  Frameshift mutations (insertions and deletion) - entire amino acid sequence effected 

  • Insertions and deletions changes cause frameshift in how mRNA is read 
  • Changes amino acid sequence -> changes polypeptide product 
  • Extent of mutation is determined at location of frameshift mutation 
  • Can causes nonsense mutations if premature stop codon forms 
• DELETION

  • Loss of a part of a chromosome.
  • Results in genes being lost.
  • Effects on growth and development.
  • FATAL

  
• DUPLICATION

  • Portion of chromosome is repeated.
  • Multiple copies of genes.
  • Can be both harmful and beneficial.

  
• INVERSION

  • Portion of chromosomes rearrange/change orientation.
  • Rotates 180 degrees and reattaches.
  • LEAST HARMFUL
• TRANSLOCTION

  • Portion of chromosome breaks off and reattaches to a different chromosome (non-homologous)
  • Occurs in pairs
  • Loss of a piece, gain of another.

   

  
•  

  INSERTION

  • Section of chromosome breaks off and attaches to another.

  
• BIOLOGICAL CONCEQUENCES OF LOW GENETIC DIVERSITY

  1. Small population + no gene flow 
  2. Increase rate of inbreeding -> reducing genetic diversity 
  3. Decreased genetic diversity -> increased chance of extinction 
• SELECTIVE BREEDING (ARTIFICAL SELECTION)

  • Humans decide which individuals may interbed based on desired trait.
  • Increase allele frequency of desired trait (Phenotype) in gene pool.
  • Only allows certain individuals to reproduce and have offspring with same trait.
• Reduces resistance to environmental change  

   Low genetic variation in population 

  1. Individuals are less able to adapt to new selection pressures (natural selection) 

  Reduces biodiversity 

  1. Low genetic variation in population 

  Increase sexual abnormalities  

  1. Low genetic variation in population 
  2. Higher inbreeding rate in a population -> increasing number of homozygous alleles in offspring 
  3. Increasing genetic abnormalities due to recessive traits 

  • Populations with low genetic variation/diversity have increased risk to extinction 
• Antigenic shift (new strain) 

  • Different strains (two or more) of a virus combine to form a new strain of virus 
  • E.g. Host is infected with two different kinds influenza A virus -> producing new variant/subtype 
• Antigenic drift (mutation) 

  • Point mutation, causing a small change.
  • E.g. Influenza virus accumulates small genetic changes over time -> producing new subtype/variant 
•  

  CONCEQUENCES OF ANTIGENIC DRIFT AND SHIFT

  Antigenic drift - partial immune response 

  1. Slight variation of influenzas strain allows partial immune response (not always variation) 
  2. This is due to only some antibody-antigen complexes forming  

   

  Antigenic shift - no immune response 

  1. The immune system identifies the virus as new -> new immune response 
  2. May produce greater risk of infection due to primary exposure 
• NATURAL SELECTION REDUCES GENETIC VARITATION

  • ELIMATES INDIVUALS WHO HAVE A SELECTIVR DISADVANTAGE
  • UNFIT PHENOTYPES.
  • Acts to stabilise allele frequencies.