Genetics of PTC Tasting
Introduction to PTC
- PTC (Phenylthiocarbamide)
- Chemical compound used in genetics classes.
- Available on paper strips known as PTC paper.
- Demonstrates genetic variation: some taste it as bitter, others taste nothing.
Genetic Basis
- Genetic Trait
- Ability to taste PTC is a genetically determined trait.
- Controlled by specific genes; can be influenced by multiple genes.
- Genes and DNA
- Genes are DNA segments coding for traits.
- Humans have 46 chromosomes: 23 from each parent.
Alleles and Inheritance
- Chromosome Pairs
- PTC taste sensitivity locus is on one chromosome pair.
- Each chromosome pair consists of one chromosome from each parent.
- Alleles
- Alleles are gene variants.
- Two alleles inherited per gene.
- Dominant alleles (represented by uppercase, e.g., T) express the trait if present.
- Recessive alleles (represented by lowercase, e.g., t) express the trait only if both alleles are recessive.
Genotypes and Phenotypes
- Genotypes
- Combinations of alleles determine the genetic makeup.
- Possible genotypes: TT, Tt, tt.
- Phenotypes
- Physical expression of genotypes.
- TT and Tt result in the ability to taste PTC (taster phenotype).
- tt results in no taste ability (non-taster phenotype).
Case Study: Personal Example
- Personal Observation
- Presenter cannot taste PTC, indicating a tt genotype.
- Both parents can taste PTC, suggesting they are Tt.
- Punnett squares can illustrate genotype probabilities.
Dominance and Trait Frequency
- Dominant vs. Recessive Traits
- Dominant traits require one dominant allele to be expressed.
- Not always more common in population than recessive traits.
- Example: Polydactyly as a dominant but rare trait.
Conclusion
- Genetics can explain variations in PTC taste sensitivity.
- Dominant traits are not necessarily the most common.
- Encourage curiosity in genetic exploration.
Note: The information and examples are inspired by a genetic explanation of PTC tasting, highlighting genetic traits and inheritance.