8.2 transfer of genetic info

• genotype


  genetic constitution of organism
• phenotype


  • expressed and observable characteristic of organism
  • due to interaction between genotype and environment
• allele


  • different forms of the same gene
  • found on the locus of a chromosome
• dominant allele


  
  

  • always expressed in organism
  • whether it has 1 allele or 2
• recessive allele


  • characteristic only appears in phenotype when no dominant alleles are present
  • must be homozygous recessive to be seen (aa)
• codominant allele


  • 2 dominant alleles contributing to the phenotype
  • via a mix or both characteristics shown together
• homozygous


  • same alleles (both dominant, AA or both recessive, aa)
• heterozygous


  • one allele is dominant and one is recessive (Aa)
• multiple alleles


  • gene with more than 2 alleles
• reading pedigree diagrams


  • if trait is dominant = one parent MUST have trait
  • if trait is recessive = neither parent has to have trait
  • if trait is sex linked or autosomal
• how to work out if trait is sex linked or autosomal?

  • autosomal = male and female have equal chance of being affected
  • sex-linked = recessive, males more affected than female
• how to tell if you are dealing with 2 non interacting unlinked genes?

  9:3:3:1 ratio - as long as both parents are heterozygous
• what is a sex linked disorder?


  • disorder caused by faulty gene
  • located on the x or y (sex) chromosome
  • making the disorder more likely for one gender.
• what is autosomal linkage?

  • 2+ genes located on same (non sex) chromosome
  • only 1 homologous pair of is needed for all 4 alleles to be present
  • for non linked genes, 2 homologous pairs are needed
• example of autosomal linkage?

  drosophila - fruit fly

  boy colour and wing length are autosomally linked, inherited in pairs
• why are autosomally linked genes inherited in pairs?

  genes on the same chromosome, are less likely to be crossed over during meiosis

  therefore they are inherited as if they are from the same gene
• what is the chi squared test?

  compares frequencies actually observed from an experiment vs the expected frequencies
• how do you carry out the chi squared test?

  o = observed frequency

  e = expected frequency (can be worked out by doing row total x column total/ overall total)

  1. calculate chi squared test
  2. calculate dof (no. of categories-1)
  3. check to see if results are significant

  
• what to write when answering stats question:

  • null hypothesis - no difference between observed and expected results
  • p value - 0.05 as results are not due to chance
  • dof - (n-1)
  • whether calculated value is higher or lower then the critical value
  • accept or reject the null hypothesis