Somatic Cells vs. Gametes

Sperm and Eggs are gametes
Sperm fertilizing an ovum. Getty/Oliver Cleve

Multicellular eukaryotic organisms can have many different types of cells that can perform different functions as they combine to form tissues. There are two main types of cells within the multicellular organism. These are called somatic cells and sex cells, or gametes.

Somatic cells

Somatic cells are a regular type of body cell that is not involved in anyway in sexual reproduction. In humans, somatic cells are diploid, meaning they have two full sets of chromosomes in them.

Somatic cells reproduce using the process of mitosis to create identical diploid copies of themselves when they split.

Other types of species may have haploid somatic cells. In these types of individuals, all of their body cells have only one set of chromosomes. This can be found in any sort of species that has a haplontic life cycle or follows the alternation of generations life cycles.

Humans begin as a single cell when the sperm and the egg fuse during fertilization to form the zygote. From there, the zygote will undergo mitosis to create more, identical cells. Eventually, these stem cells will undergo differentiation to create different types of somatic cells. Depending on the time of differentiation and the cells' exposure to different environments as they develop, the cells begin down different life paths to create all of the differently functioning cells in the human body.

Humans have more than three trillion cells as an adult.

The somatic cells make up the bulk of that number. The somatic cells that have differentiated can become adult neurons in the nervous system, blood cells in the cardiovascular system, liver cells in the digestive system, or many, many more types throughout the entire body and every body system.

Sometimes, during replication, mistakes can be made.

These mutations can change the DNA in the cells of the body. However, if there is a mutation in a somatic cell, it most likely will not contribute to the evolution of the species. Since somatic cells are in no way involved in the process of sexual reproduction, any changes in the DNA of somatic cells will not get passed down to the offspring of the mutated parent. Since the offspring will not receive the changed DNA and any new traits the parent may have will not be passed down, mutations in the DNA of somatic cells will not cause evolution.

Gametes

Almost all multicellular eukaryotic organisms that undergo sexual reproduction use gametes, or sex cells, to create offspring. Since two parents are necessary to create individuals for the next generation of the species, gametes are typically haploid cells. That way, each parent can contribute half of the total DNA to the offspring. When two haploid gametes fuse during sexual reproduction fertilization, they each contribute one set of chromosomes to make the single diploid zygote that has a full two sets of chromosomes.

In humans, the gametes are called the sperm (in the male) and the egg (in the female). These are formed from the process of meiosis, which can take a diploid cell and make four haploid gametes at the end of meiosis II.

While a human male can continue to make new gametes throughout his life starting at puberty, the human female has a limited number of gametes she can make within a relatively short amount of time.

If there happens to be a mutation in a gamete, that can drive evolution. Mistakes can happen during meiosis that can either change the DNA in the haploid cells, or create a chromosome mutation which can add or delete portions of DNA on various chromosomes. If one of the offspring is created from a gamete that has a mutation in it, then that offspring will have different traits that may or may not be favorable for the environment. Natural selection will "choose" which mutations are favorable and which are not. This process drives evolution.