Germ theory

Germ Plasm is a concept in developmental biology that proposes that multicellular organisms consist of two fundamental cell types: somatic cells and germ cells. This theory was first proposed by the German biologist August Weismann in the late 19th century.

History

The germ plasm theory was first proposed by August Weismann in 1892. Weismann suggested that the hereditary material, which he termed the germ plasm, is separate and distinct from the rest of the body, or soma. This was a significant departure from the prevailing theory of the time, which held that all cells contribute to the hereditary material.

Concept

According to the germ plasm theory, the germ cells (which develop into eggs or sperm) contain a complete set of genetic information that is passed on to the offspring. The somatic cells, on the other hand, are responsible for the development and maintenance of the body but do not contribute to the genetic makeup of the offspring.

This theory is supported by the observation that only germ cells, and not somatic cells, undergo meiosis – a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell. This is in contrast to mitosis, the process by which most cells divide, which results in two daughter cells each with the same number of chromosomes as the parent cell.

Implications

The germ plasm theory has significant implications for our understanding of genetics and evolution. It suggests that changes in the somatic cells of an organism – for example, as a result of environmental influences – cannot be passed on to the offspring. This is in contrast to the theory of Lamarckism, which proposes that characteristics acquired or lost during an organism's lifetime can be inherited.

The germ plasm theory also has implications for the field of reproductive medicine. It suggests that treatments or interventions that affect the somatic cells of an individual will not have an impact on their genetic offspring.

Criticisms

While the germ plasm theory is widely accepted, it has been subject to some criticism. Some scientists argue that there is evidence of epigenetic inheritance – the transmission of information from parent to offspring that is not encoded in the DNA sequence. This suggests that the distinction between germ cells and somatic cells may not be as clear-cut as the germ plasm theory suggests.

See also

• Cell biology
• Genetic inheritance
• Epigenetics