The correct answer to explain why the son has red hair when both parents have brown hair is Mendel’s Law of Segregation.
The most relevant principle in this context is Mendel’s Law of Segregation. According to this law, allele pairs separate or segregate during gamete formation, and randomly unite at fertilization. This means that a child inherits one allele for each trait from each parent.
In this scenario, red hair is a recessive trait, while brown hair is a dominant trait. Both parents have brown hair, but since the son has red hair, each parent must have carried one allele for red hair and one for brown hair. They both passed the red hair allele to their son.
This is a classic example of how recessive traits can be expressed in the phenotype of an individual when two carriers reproduce.
The other laws listed are not as directly applicable to this specific question:
- Mendel’s Law of Dominance explains that one allele can mask the presence of another, which doesn't directly explain the presence of red hair since that is a recessive trait.
- Mendel’s Law of Probabilities deals with the likelihood of different outcomes, but doesn't explain the mechanism behind the son's red hair.
- Mendel’s Law of Inheritance is not one of Mendel's laws, rather, it is a general term that could be used to describe all of his findings.