6.2 Patterns of Inheritance

• Codominant


  both alleles are equally dominant and will both be expressed as the phenotype
• Multiple alleles 


  more than two alleles for a single gene
• Sex Linkage 


  gene whose locus is on the X chromosomes
• Autosomal linkage 


  genes that are located on the same chromosome (not the sex-chromosome). not by chance. Linked alleles are inherited together
• Epistasis 


  one gene modifies or masks the expression of a different gene at a different locus
• Monohybrid 


  genetic inheritance of a characteristic determined by one gene
• Dihybrid 


  genetic inheritance for a characteristic determined by two genes
• Chi-squared test

  finds the statistical difference between the observed and expected data.

  A) O

  B) - E

  C) E

  D) Observed

  E) Expected

  
• Discontinuous Variation 


  characteristics determined by one gene - monogenic inheritance
• Continuous Variation

  characteristics determined by more than one gene - polygenic inheritance
• Stabilising selection

  1. Environment does not change
  2. Natural selection favours average phenotype, against extreme phenotypes
  3. Individuals closest to the mean are favoured
  4. low diversty
• Direction Selection

  1. Environmental conditions have changed
  2. natural selection favours one extreme phenotype
  3. the mean will move towards the characteristics
• Genetic Drift

  1. changes in a populations allele frequencies due to chance
• Genetic bottleneck

  1. catastrophic event dramatically reduces the size of the population
  2. decreases the variety of alleles in the gene pool
• Founder Effect

  1. small number of individuals become isloated
  2. new population with limited gene pool
  3. alleles not reflective of the original population
• Hardy-Weinberg Principle

  estimate the frequency of alleles in a population
• Assumptions of the Hardy-Weinberg principle

  1. population large enough to make the sampling error negligible
  2. mating was random
  3. no selective advantage for any genotype
  4. no mutation, migration or genetic drift
• What is speciation

  Genetic makeup of populations changes to the extent the two groups can no longer interbreed - they have become separate species
• Allotropic Speciation

  1. Geographical isolation
  2. physical barrier - lakes, rivers, oceans, mountains
  3. different selection pressures
  4. different alleles are favoured
  5. natural selection
• Sympatric speciation

  1. reproductive isolation
  2. changes to anatomy or behaviour that may prevent breeding
  3. Courtship behaviour - time of year they mate
  4. animal genitalia/flower structure
• Artificial selection

  humans choosing desired phenotypes and breeding animals that display these characteristics to produce offspring with these desired characteristics. Increases genetic disorders due to interbreeding and low genetic diversity
• Chi-squared

  1. Degree of freedom; number of categories - 1
  2. Critical value
  3. If chi value less than critical - accept null hypothesis, no significant difference, due to chance
  4. if chi value greater than critical, reject null hypothesis there is a significant difference, due to external factor
• causes of genetic variation

  1. mutation
  2. Recombination - genes on homologous chromosomes are reshuffled, new combinations of genes
• Selection?

  Stabilising

  
• Selection?

  Directional

  
• How can an allele mask/modify the expression of another (epsistais)

  1. Produces a repressor protein which binds to ribosome
  2. prevents transcription
  3. inhibit the enzyme