Lecture Notes: Genetics and PTC Taste Sensitivity

Introduction

• PTC (Phenylthiocarbamide): Chemical used in genetic experiments
  • Sold on paper strips (PTC paper)
  • Some people taste it as very bitter; others taste nothing
• Personal anecdote: Couldn't taste PTC, felt left out in class

Genetic Basis of PTC Tasting

• Genes: Portions of DNA that code for traits
• Trait: PTC taste sensitivity
• Some traits are influenced by multiple genes (e.g., eye color)
• PTC taste sensitivity potentially involves multiple genes but is heavily impacted by one specific gene

Chromosomes and Alleles

• Humans have 46 chromosomes (23 pairs)
• Chromosomes are made of DNA and protein
• Inheritance: 23 chromosomes from each parent
• Locus: Specific location on a chromosome where a gene is found
• Alleles: Variants of a gene
  • Can be the same or different
• Parents each contribute one allele

PTC Taste Sensitivity Breakdown

• Alleles for PTC:
  • Dominant (T): Ability to taste PTC
  • Recessive (t): Inability to taste PTC
• Genotypes:
  • TT: Taster
  • Tt: Taster
  • tt: Non-taster
• Phenotypes:
  • Taster: Requires at least one T allele
  • Non-taster: Requires tt genotype

Example with Personal Anecdote

• Parents: Both could taste PTC (Tt genotype)
• Offspring (Me): Non-taster (tt genotype)
• Explanation: Inherited one recessive allele (t) from each parent

Punnett Squares

• Tool to determine probabilities of offspring genotypes
• Used in predicting genetic inheritance
• To be covered in another video

Dominant vs Recessive Traits

• Common Misconception: Dominant traits are not always more common in a population
  • Example: Polydactyly (extra fingers)
    • Dominant trait but rare occurrence

Conclusion

• Importance of genetics in understanding traits
• Stay curious!