11.2 - Probability

• • A lot of genetics is about trying to figure out the likelihood that a trait will appear - this is called probability
  • Punnett Squares can be used to figure out the probability of genetic combinations occurring in a cross between two parents
  • A punnett square doesn't tell what will actually happen in a cross, just the likeliness of an event happening or that a result can happen
  • Ex: a family of 6 kids should have 3 boys and 3 girls
• Key terms:

  • Trait: a characterisitic
  • Ex: plant height, a needed enzyme
  • Phenotype: the physical form of a trait
  • Ex: tall or short plant
  • Genotype: the two genes that make-up a trait
  • Ex: TT, Tt, tt
• For most traits, an organisms has two genes, one from each parent, so the allele combinations for trait could be:

  • TT& Tt = tall plant
  • tt = short plant
  • Homozygous dominant = two dom. alleles
  • genotype: TT (all caps!)
  • Heterozygous dominant = one dom. & one rec. allele
  • genotype: Tt
  • Recessive = two rec. alleles
  • genotype: tt (all lowercase!)