Problem 5 - 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 has high sensitivity to PTC; he could be TT or Tt.

Step 1: Understanding Sensitivity to PTC

Sensitivity to the taste of Phenylthiocarbamide (PTC) is a genetic trait controlled by a single gene. It follows a dominant-recessive inheritance pattern, where the ability to taste PTC is dominant (T) and the inability to taste PTC is recessive (t).

Step 2: Analyzing Your Genotype

Since you have a high sensitivity to PTC, your genotype must include at least one dominant allele (T). This means you could be either homozygous dominant (TT) or heterozygous (Tt).

Step 3: Analyzing Your Mother's Genotype

Your mother has low sensitivity to the taste of PTC. Hence, her genotype must be homozygous recessive (tt), as she can only pass on the recessive allele to her children.

Step 4: Deductions About Your Father's Genotype

Given that you must have one dominant allele (T) to taste PTC and your mother can only pass on recessive alleles (t), your father must have contributed the dominant allele (T) to you. Hence, your father has high sensitivity to PTC and his genotype could either be homozygous dominant (TT) or heterozygous (Tt).

Key Concepts

Dominant-recessive inheritance

Dominant-recessive inheritance is a fundamental concept in genetics that explains how certain traits are passed down from parents to offspring. In this type of inheritance:

• A dominant allele is one that expresses its trait even if only one copy is present in the genotype. It is represented by an uppercase letter, such as 'T'.
• A recessive allele only expresses its trait if two copies are present (homozygous recessive), represented by a lowercase letter, like 't'.

The presence of a dominant allele (T) masks the expression of a recessive allele (t). If an organism inherits one dominant and one recessive allele (Tt), the dominant trait will be observed. This pattern is seen in the sensitivity to Phenylthiocarbamide (PTC) tasting, where tasting ability is dominant. Knowing the difference between dominant and recessive alleles helps in predicting the traits of offspring based on parental genotypes.

Phenylthiocarbamide (PTC)

Phenylthiocarbamide (PTC) is a chemical compound that is often used in genetic studies regarding taste sensitivity. Its bitter taste can be detected by some people, but not by others, based on their genetic makeup.

Sensitivity to PTC falls under a dominant-recessive inheritance pattern, where:

• Individuals with at least one dominant allele (T) can taste the bitterness, making them PTC tasters.
• Individuals with two recessive alleles (tt) cannot taste PTC, classifying them as non-tasters.

This variation in taste ability makes PTC an interesting tool for studying genetics, as it can directly illustrate the effects of genetic inheritance. It's a fascinating example of how a simple molecule can reveal insights into our genetic differences.

Genotype

The term "genotype" refers to the genetic makeup of an individual with regard to a particular trait. For PTC sensitivity, the genotype determines whether a person is a taster or a non-taster.

There are three possible genotypes for this trait:

• Homozygous dominant (TT): The individual has two dominant alleles, ensuring high sensitivity to PTC.
• Heterozygous (Tt): The individual has one dominant and one recessive allele, which also results in tasting PTC due to the presence of the dominant allele.
• Homozygous recessive (tt): The individual has two recessive alleles, leading to no sensitivity to PTC.

Understanding genotypes leads to better comprehension of how traits are passed down and can be used to predict the probability of an offspring inheriting certain traits from the parents.