Lecture Notes: Genetics and PTC Taste Sensitivity

Introduction to PTC Taste Sensitivity

• PTC: A chemical used in genetic classes on paper strips.
• Experience: People either taste it as bitter or taste nothing.
  • Personal anecdote of not being able to taste PTC.

Genetics Behind PTC Taste Sensitivity

• Genes and Traits:
  • Genes are portions of DNA coding for traits (e.g., PTC taste sensitivity).
  • Some traits involve multiple genes (e.g., eye color).
• PTC Taste Sensitivity:
  • Controlled by a specific gene with potential interactions from other genes.

Chromosomes and Alleles

• Human Chromosomes:
  • Humans have 46 chromosomes (23 pairs).
  • Inherit 23 chromosomes from each parent.
• Alleles:
  • Variants of a gene; can be the same or different.
  • Affect traits such as PTC taste sensitivity.

Genotypes and Phenotypes

• Genotypes:
  • Represented by alleles: TT, Tt, tt.
  • Capital letter (T) indicates a dominant allele; lowercase (t) is recessive.
• Phenotypes:
  • Physical expression of genotypes.
  • Tasting PTC is a dominant trait.

Dominant and Recessive Traits

• Dominant Trait:
  • Expressed with at least one dominant allele.
  • Taster phenotype: TT or Tt.
• Recessive Trait:
  • Expressed only with two recessive alleles (tt).
  • Non-taster phenotype.

Parental Genotypes and Punnett Squares

• Parental Genotypes:
  • To have a non-taster child (tt) from taster parents, both parents must be Tt.
• Punnett Squares:
  • Used to determine probabilities of offspring genotypes and phenotypes.

Common Misconceptions

• Dominant Traits Not Always Common:
  • Dominant traits aren't always more common due to allele frequency.
  • Example: Polydactyly is a dominant but rare trait.

Conclusion

• Encouragement to stay curious about genetics.