Problem 2 - Biological Psychology

Question

Suppose you have high sensitivity to the taste of PTC. If your mother has low sensitivity, what (if anything) can you predict about your father's taste sensitivity?

Step-by-Step Solution

Answer

Your father must have high sensitivity to PTC.

Step 1: Understand the Genetic Basis

The ability to taste PTC (phenylthiocarbamide) is often used as an example of a simple Mendelian trait, where high sensitivity is a dominant trait (T) and low sensitivity is recessive (t). Individuals with at least one T allele (TT or Tt) will have high sensitivity, while those with tt will have low sensitivity.

Step 2: Analyze Your Genotype

Given that you have high sensitivity to PTC, your genotype is either TT or Tt. Since only one T allele is needed to exhibit the trait, your genotype cannot be definitively determined just yet.

Step 3: Consider Mother's Genotype

The mother has low sensitivity to PTC, meaning her genotype must be tt (both alleles recessive) since low sensitivity is a recessive trait. Since you are highly sensitive, you must have received one T allele from your father.

Step 4: Predict Father's Genotype

Since your mother can only provide a t allele (because she is tt), you must have received the T allele from your father. Therefore, your father's genotype must include at least one T allele, making his genotype either TT or Tt. This means your father must have high sensitivity to PTC.

Key Concepts

Phenylthiocarbamide (PTC)

Phenylthiocarbamide, or PTC, is a synthetic compound that is commonly used in genetics to study taste sensitivity. This compound is either bitter or tasteless depending on one's genetic makeup.
PTC tasting is controlled by a single gene, which determines whether an individual can taste PTC as bitter (and intensely so for some) or not at all. This makes it a classic example for studying Mendelian inheritance, where traits are passed on from parents to offspring.
The ability to taste PTC depends on the presence of a particular allele of the PTC gene. People who can taste PTC have at least one copy of the T (taster) allele. Those who can't taste it possess two copies of the recessive t (non-taster) allele.

• PTC tasting is linked to variations in taste receptor genes.
• The PTC gene is located on chromosome 7 in humans.
• Understanding PTC tasting genes can provide insights into other taste sensitivities and even dietary preferences.

Studying PTC tastability not only aids in understanding genetic traits but also serves as a model for certain complex taste and dietary behaviors in humans.

Dominant Trait

In the context of PTC tasting, the dominant trait is characterized by the presence of the T allele, which signifies high sensitivity to PTC, leading to a bitter taste sensation.
Dominance in genetics refers to the allele that is expressed in the phenotype even when only one copy is present. Here, having one T allele (heterozygous condition, Tt) is sufficient for an individual to taste PTC.
In simple terms, if a person has either TT or Tt genotype, they will express the dominant trait and be able to taste PTC.

• The presence of a single T allele is enough to override the effects of a t allele if it is present.
• In genetics, dominant traits only require one dominant allele to be expressed.
• Dominant traits can often mask the presence of recessive alleles.

Recognizing which traits are dominant is vital for predicting patterns of inheritance and understanding genetic variation within a population.

Genotype Analysis

Genotype analysis involves determining the genetic makeup of an individual by identifying the alleles they possess. This analysis is crucial for predicting inherited traits and understanding family genetics.
In the PTC tasting scenario, determining your genotype provides insights into what alleles you carry related to PTC taste sensitivity. Given that high sensitivity (dominant trait) is observed, the possible genotypes are TT or Tt.
Since the mother has a tt genotype, indicating low sensitivity, it confirms that you inherited one recessive t allele from her. Therefore, the T allele must have come from the father, confirming he has a T allele as part of his genotype.

• Determining genotypes helps trace allele distribution in familial lines.
• Genotype analysis is used in predicting possible offspring traits.
• Interpreting the genotype can provide detailed genetic and hereditary insights.

Genotype analysis is a fundamental tool in genetics used to interpret how traits are inherited and to assess potential genetic outcomes.