Mitochondria are large organelle found in the cytoplasm of the cell, contains their own DNA. Let us explore about the inheritance of mitochondrial DNA.
The mitochondrial DNA is inherited. However, the nuclear DNA is also inherited, it is highly packed in 46 chromosomes, of which half of them comes from mother and half from father. But mitochondrial DNA comes only from one parent.
Mitochondria can replicate itself without following instructions from the nucleus and has the ability to get inherited from one generation to the next.
How is mitochondrial DNA inherited?
Mitochondria is present in each and every type of cell, so it becomes easy for them to get inherited. Let us find out how mitochondrial DNA is inherited.
Mitochondrial DNA follows the mechanism of simple dilution for inheritance. Male mitochondrial DNA is degraded in male genital system and some are degraded in female genital tract. When nuclear DNA separates half of its chromosomes, mitochondrial DNA also get packed and pass along with gametes.
Mitochondrial DNA is inherited by its own. The Oocyte contains numerous amount of mitochondria and it is passed to the offspring during zygote formation.
When mitochondrial DNA is inherited?
Mitochondrial DNA is circular and found free in the matrix like in prokaryotes. Let us find out when mitochondrial DNA is inherited.
During the fertilization of male and female gametes, mitochondrial DNA gets inherited in the offspring. Mitochondria are uniformly distributed in unspecialized cells.
Mitochondria has its own genome and can replicate by its own without depending upon the nuclear genome. In mammals, mitochondria replicate and forms number of copies after fertilization of gametes and covers almost each and every cell. They move about in cytoplasm of each cell.
Is mitochondrial DNA inherited from the father?
Male sperm has less mitochondria in number while female ova contains mitochondria in a large number. Let us find out who contributes the mitochondrial DNA to the offspring.
Mitochondrial DNA is not inherited from father. It is only inherited from mother because during fertilization, only head of the sperm containing nucleus enters inside the ova or eggs.
However, the size of ova is bigger than the sperm. Ova contains numerous amount of mitochondria and sperms have limited mitochondria which is found at the neck region of sperm. Therefore, it is not possible for the paternal mitochondria to enter inside the egg.
Why do males not pass on mitochondrial DNA?
One theory suggest that in some cases male can pass their mitochondria to their offspring along with their nuclear DNA. Let us find out the exact reason behind this.
Male sperms contains approximately 50-75 mitochondria in their tail region. When sperm fuses with the egg, the tail dissolves after conception. Therefore, males cannot pass their mitochondrial DNA to their offspring.
After conception, ova contains thousands of mitochondria. Each mitochondria contains multiple copies of mitochondrial DNA. Each mitochondria is independent of each other. As the zygotes divides further, these mitochondria also get divided into the cells of the developing embryo.
By the time, our body cells divide into tissues and organs, variations occurs in mitochondrial DNA and scatters all around the body cells.
Is mitochondrial DNA inherited from the mother?
Nuclear DNA is inherited from both the parents. Lets us find out from which parent mitochondrial DNA is transmitted to the offspring.
Mitochondrial DNA is inherited from the mother only. The number of mitochondria in females are much higher than the males. The exact mechanism for the inheritance of mitochondrial DNA from mother is still unknown.
Why is mitochondrial DNA inherited only from the mother
During fertilization, both the gametes contain mitochondria but offspring receives only maternal mitochondria. Let us find out the reason below.
Mitochondrial DNA is only inherited from mother because paternal mitochondria in the tail of the sperm gets dissolved outside the ovum. That is why only mitochondria from ovum passes on to their offspring.
When the fusion of both male and female gametes occur, sperm from father cannot fuse completely because it has lost all the energy by pushing the head of the sperm. The tail of the sperm eventually diminishes or dissolves by enzyme proteosome.
Do siblings have the same mitochondrial DNA?
In male and female offspring, mitochondrial DNA carries traits inherited from a mother. Let us explore about the siblings mitochondrial DNA.
Siblings contain the same mitochondrial DNA. Mitochondria has its own genome and characteristic features that are inherited from the mother to their offspring. Therefore, inherited mitochondrial DNA is same in the siblings if the maternal lineage is not broken.
Individuals from the same maternal line cannot be distinguished by mitochondrial DNA test because all the inherited mitochondrial DNA is same in each individual so it becomes impossible to find out who is mother, daughter, grand mother etc.
Functions of Mitochondrial DNA
Mitochondrial DNA is completely functional. Let us discover more functions of mitochondria and its DNA.
Some of the functions performed by mitochondrial DNA are listed below –
- Mitochondrial DNA helps to to regulate the cellular metabolism, apoptosis and oxidative stress control.
- Mitochondrial DNA covers almost 16,500 DNA basepairs of the total DNA .
- Mitochondria are semi-autonomous, their structure and working are partially controlled by the nucleus.
- Mitochondria contains about 37 genes, out of which 13 genes are specifically associated in the oxidative phosphorylation.
- Mitochondria is called the Power house of the cell because it is the main site for the ATP synthesis.
- Ribosomes of mitochondrial DNA manufactures some component of the mitochondrial enzyme and rest components are obtained from cytosol under the instructions from the cell nucleus.
- The frequency of polymorphisms and mutations in mitochondrial DNA is very high.
- Mitochondrial DNA helps in the synthesis of essential enzymes required for the production of ATP.
- Mitochondrial DNA is able to replicate itself and can produce all three types of RNA from its DNA – rRNA, mRNA and tRNA.
- Some structural proteins are manufactured by mitochondrion over its own ribosomes and are incorporated in the inner membrane.
What is Mitochondrial DNA bottleneck hypothesis?
When mutation occurs, it can affect the mitochondrial DNA in each cell (Heteroplasmy). Let us read some more information about bottleneck hypothesis below.
Heteroplasmic mutated mitochondrial DNA is inherited from the mother in their offspring. The sudden changes in the frequency of genes of the offspring from one generation to the next constitutes bottleneck hypothesis.
A single egg contains less amount of mutant mitochondrial DNA but when it becomes embryo, the mutant load varies in different cells. Cell selection remove or exclude the higher mutant cells in order to stabilize the mutant load between generations.
To wrap up this post, we can conclude that mitochondrial DNA is independent of nuclear DNA and it is inherited from mother only. Theories are given that some organisms may inherit mitochondrial DNA from both parents but usually in mammals, plants and fungi, it is from only one parent. It is also true that some of the functions of mitochondria are partially regulated by the cell nucleus.