What Is the Law of Dominance of Traits? Explain with an Example

Introduction

The Law of Dominance of Traits is one of the fundamental principles of genetics. This law states that one gene of a gene pair will be dominant, while the other will be recessive. This means that only the dominant gene will be expressed in the phenotype, while the recessive gene will remain hidden.

The content discusses the Law of Dominance of Traits is, how it works, and provides examples to help illustrate this concept.

Understanding the Law of Dominance of Traits

The Law of Dominance of Traits was first proposed by Gregor Mendel, a scientist, and monk who is considered the father of modern genetics. In his experiments with pea plants, Mendel observed that certain traits, such as flower color or seed shape, were always expressed in the offspring of the pea plants, while others were not.

Through his experiments, Mendel discovered that these traits were controlled by genes, which were passed down from parents to offspring. He also discovered that each gene existed in two forms, or alleles, one dominant and one recessive.

The dominant allele was expressed in the phenotype, while the recessive allele remained hidden. This meant that even if an organism had a recessive allele for a certain trait, it would not be expressed unless it inherited two copies of the recessive allele.

This concept can be illustrated using the example of flower color in pea plants. Mendel observed that some pea plants had purple flowers, while others had white flowers. He hypothesized that there were two alleles for flower color, one for purple and one for white.

When Mendel crossed a purple-flowered plant with a white-flowered plant, he found that all of the offspring had purple flowers. This was because the allele for purple flowers was dominant, and the allele for white flowers was recessive.

However, when Mendel crossed two of these purple-flowered offspring, he found that some of the resulting offspring had white flowers. This was because some of these offspring inherited two copies of the recessive allele for white flowers, while others inherited one dominant allele and one recessive allele for purple flowers.

This example illustrates how the Law of Dominance of Traits works. The dominant allele is expressed in the phenotype, while the recessive allele remains hidden unless an organism inherits two copies of it.

Exceptions to the Law of Dominance of Traits

While the Law of Dominance of Traits is a fundamental principle of genetics, there are some exceptions to this law. One of these exceptions is incomplete dominance.

In incomplete dominance, neither allele is completely dominant nor recessive, and the phenotype of the offspring is a blend of the two parental phenotypes. For example, when a red-flowered plant is crossed with a white-flowered plant, the resulting offspring may have pink flowers, which is a blend of the two parental colors.

Another exception to the Law of Dominance of Traits is codominance. In codominance, both alleles are expressed in the phenotype of the offspring. For example, when a black-feathered chicken is crossed with a white-feathered chicken, the resulting offspring may have both black and white feathers.

Examples of the Law of Dominance of Traits in Humans

The Law of Dominance of Traits applies not just to pea plants, but also to humans. There are many traits in humans that are controlled by dominant and recessive alleles.

One example is earlobe attachment. The allele for free earlobes is dominant, while the allele for attached earlobes is recessive. This means that an individual with one allele for free earlobes and one allele for attached earlobes will have free earlobes because the allele for free earlobes is dominant.

Another example is tongue-rolling. The ability to roll your tongue is controlled by a dominant allele, while the inability to roll your tongue is controlled by a recessive allele. This means that an individual with one allele for tongue rolling and one allele for not being able to roll their tongue will still be able to roll their tongue because the allele for tongue rolling is dominant.

A third example is Huntington's disease, a genetic disorder that causes the progressive breakdown of nerve cells in the brain. The allele for Huntington's disease is dominant, meaning that an individual with just one copy of the gene will develop the disease.

Conclusion

The Law of Dominance of Traits is a fundamental principle of genetics that explains how certain traits are expressed in offspring. This law states that one gene of a gene pair will be dominant, while the other will be recessive. This means that only the dominant gene will be expressed in the phenotype, while the recessive gene will remain hidden.

While there are exceptions to this law, such as incomplete dominance and codominance, the Law of Dominance of Traits still provides a useful framework for understanding how genes are passed down from parents to offspring.

By studying the Law of Dominance of Traits and other principles of genetics, scientists can gain a better understanding of how genetic disorders develop and how they can be treated. This knowledge can also help us make informed decisions about our own health and the health of our children.