Question

As discussed in Chapter 25, most forms of cancer are caused by environmental agents that produce mutations in somatic cells. Is an individual with cancer considered a genctic mosaic? Explain why or why not.

Short answer

Yes, an individual with cancer can be considered a genetic mosaic as they have some cells (the cancerous cells) which have a different genetic makeup due to mutations, existing alongside healthy cells within the same individual.

Step-by-step solution

Defining a Genetic Mosaic

Genetic mosaicism refers to the condition where cells within the same person's body have a different genetic makeup. This typically happens when there are changes or mutations that occur after fertilization during an organism's development.

Understanding How Cancer Develops

Cancer develops when there are mutations in somatic cells that cause the cells to grow and divide uncontrollably. These mutated cells form a tumor, where each cell in the tumor would share the same genetic mutation.

Applying the Definition of Genetic Mosaicism to Cancer

Because the tumor cells have a different genetic makeup from the rest of the person's healthy cells due to mutations, and they exist within the same organism, an individual with cancer could be considered a genetic mosaic.

Key concepts

Understanding Somatic Cell Mutations

Somatic cell mutations are changes that occur in the DNA of cells that make up the tissues and organs of our bodies, excluding the reproductive cells or germ cells. Unlike hereditary mutations that are passed from parents to offspring, somatic mutations occur after fertilization and are not inherited by the next generation. These mutations can happen due to a variety of factors such as environmental influences, like exposure to radiation or carcinogenic chemicals, or errors during cell division.

An example of how somatic mutations can impact health is through the formation of moles on the skin. While most are harmless, some can undergo further mutations that turn them malignant, leading to skin cancer. This illustrates the nature of somatic mutations: they can be benign and without consequence, or they can accumulate and lead to diseases, such as cancer.

Cancer Development

Cancer is fundamentally a disease of uncontrolled cell growth triggered by mutations in genes that regulate cell division and death. These mutations can lead to the cells becoming immortal, so to speak, dividing endlessly and avoiding the natural process of cell death known as apoptosis. As these abnormal cells accumulate, they form a mass called a tumor. Tumors can either be benign, meaning they don't invade other tissues, or malignant, which can spread to other parts of the body in a process called metastasis.

It is the malignant tumors that are particularly dangerous and are classified as cancers. The journey from a single mutated cell to a full-blown cancer involves several steps - the mutations must confer some sort of survival advantage to the cells, allowing them to outcompete healthy cells and evade the immune system. This complex process is what makes cancer development so difficult to prevent and treat.

Genetic Makeup Differences in Mosaicism

In genetic mosaicism, different populations of cells have different genomes within the same organism. This intriguing phenomenon can happen as a result of mutations that occur during cell division after fertilization. Genetic mosaicism can manifest in various forms, from harmless patches of skin with different pigmentation to significant conditions like Turner syndrome, which affects sex chromosome composition in females.

Such diversity in genetic makeup can make diagnosing and treating genetic diseases more complex, as not all cells in the body will respond the same way to therapeutic interventions. As seen with occurrences of cancer, where tumor cells differ genetically from the rest of the body's cells, this variation within an organism's own tissues suggests that each individual is surprisingly unique on a cellular level.