Lisa has taught at all levels from kindergarten to college and has a master's degree in human relations.
Where is the genetic material, or DNA, located in a cell? Most likely your answer to this is that DNA is found in the cell's nucleus. Of course, this answer is correct. This is called nuclear DNA. In every basic biology class, you learn about how a cell reproduces as the DNA in the nucleus is replicated and the cell splits into two identical copies of itself.
You probably also know how the sex cells carry a copy of half of each parent's DNA in their nucleus that comes together to create a complete set of DNA in their offspring. You may even have an understanding of how dominant traits are expressed and recessive traits are not. But did you know that DNA can be found in other parts of a cell and that this genetic material can be inherited as well?
DNA found outside of the nucleus is called extranuclear DNA. It is also sometimes called cytoplasmic DNA. Many specialized structures in addition to the nucleus work within a living cell. These are called organelles. Some of these organelles found in the cytoplasm of the cell, like mitochondria or chloroplasts, also contain DNA. The replication of the DNA found within these organelles occurs separately from cell division. Instead, the organelles produce copies of themselves within the cell as needed.
Copies of the parent's original organelles are actually passed on to offspring. In this way, extranuclear DNA is inherited. As we continue the lesson, we will look at three common types of extranuclear inheritance.
One type of extranuclear inheritance is uniparental inheritance, which means the extranuclear DNA is only inherited from one parent. This occurs with sexual reproduction and is the most common form of extranuclear inheritance. An example you may have heard of is the maternal inheritance of mitochondrial DNA in humans. This extranuclear DNA is only inherited from the mother because the egg cell contains the mitochondria in its cytoplasm. The father's sperm cell does not contribute mitochondria when it joins with the mother's egg cell. In other words, you will have the same mitochondrial DNA as your mother.
Biparental inheritance is another form of extranuclear inheritance that occurs when extranuclear DNA comes from both parents. This is most likely to occur in plants that have a haploid life cycle, where they make copies of themselves with half of the nuclear DNA. If two compatible haploid cells come into contact with one another, they fuse and create a new plant with a complete set of nuclear DNA. However, organelles are passed on from both haploid cells, in this case, and the plant has a mixture of extranuclear DNA from both parents.
Vegetative segregation can also occur. This type of extranuclear inheritance happens most often during asexual reproduction. Only one parent cell exists, in this case, so all of the extranuclear DNA comes from the organelles that are within the cytoplasm of this cell. The cytoplasm is separated during cell division, and whatever extranuclear DNA is included in a particular daughter cell is what will be inherited. Since the cell may contain organelles with different DNA, and the organelles are separated at random, daughter cells may not have the same extranuclear DNA.
DNA found in the nucleus of a cell is called nuclear DNA. DNA can also be found within a cell outside of the nucleus. In this case, it is called extranuclear DNA or cytoplasmic DNA and is found within organelles such as mitochondria or chloroplasts. This DNA replicates separately from the division of a cell, but extranuclear inheritance still occurs because this DNA is also passed on to offspring.
Three types of extranuclear inheritance are uniparental inheritance, biparental inheritance, and vegetative segregation. Uniparental inheritance occurs when extranuclear DNA is inherited from only one parent. Biparental inheritance is when two parents contribute extranuclear DNA. When only one parent cell exists and has it's extranuclear DNA randomly separated between daughter cells during cell division it is called vegetative segregation.
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