Mitochondrial genetics. Are there really only maternally inherited mitochondria in our cells? What happens if paternal mitochondria happen to be present in the autosomal/germ cells? Is maternal mtDNA inheritance a universal mechanism that works for the en

Authors Avatar

Natalia Iliyashenko

Animal developmental Biology

Final Paper

Hypothesis.

Mothers pass on mitochondrial DNA (mtDNA) to their offspring. Paternal mtDNA is considered to cause abnormalities in the most mammalian and human organisms.

Research Question.

Is it true?  Are there really only maternally inherited mitochondria in our cells? What happens if paternal mitochondria happen to be present in the autosomal/germ cells? Is maternal mtDNA inheritance a universal mechanism that works for the entire living creatures and what are the benefits?

Mitochondrion is an organelle with a specific subset of its own DNA (mtDNA), which different from chromosomal DNA in most organisms. Its DNA is a plasmid, - an unwrapped circular bacterial DNA molecule. According to the recent hypotheses, a mitochondrion as a bacterium had potentially merged with the single eukaryotic cell to form symbiotic relationships. These ‘infected’ cells had further formed organisms – ancestors of present species.  Organisms had inherited mitochondria through thousands of years. One of the most interesting observations made by recent studies is the pattern of mtDNA inheritance in humans and most eukaryotic multicellular organisms excluding hybrids (interspecific crosses) and plants (Foley, 2003; Hayashida, 2005). In humans it is strictly a mother who passes mtDNA on to the offspring, while hybrids receive and

express both maternal and paternal inheritance in different tissues (Ankel-Simons, Cummins, 1996; Brandon et. al 2005; Cables, 2002; Danan, 1999; Foley, 2003;

Hayashida et al, 2005; Kunchithapadam, 1995); Whittle, Jonston, 2002).

There are a small number of lineages that can be traced down to our common ancestor – the ‘Mitochondrial Eve’. Our mtDNA is identical to that of our mothers and almost identical to the Mitochondrial Eve’s mtDNA. As normal DNA, mtDNA mutates occasionally, switching one base (A, C, G or T) to another. So, mtDNA slowly diverges from that of Mitochondrial Eve at a rate proportional to the amount of time that has passed since the Mitochondrial Eve’s existence. She was the one who had originated direct maternal mitochondrial inheritance in the offspring (Kunchithapadam, 1995).  

Several hypotheses can explain maternal mtDNA inheritance:

  1. Maternal mtDNA is not highly mutational in humans compared to mammals. It undergoes a bottleneck (mutations) only before the oogenesis (division of an egg) and does not alter throughout the fetus – adult life. Paternal mtDNA continues to mutate after the sperm formation as well, which would make a fetus a non-stable structure in terms of potential diseases that develop in adulthood, etc. (Ankel-Simons, Cummins, 1996; Brandon et. al 2005; Danan, 1999; Foley, 2003; Hayashida et al, 2005; Kunchithapadam, 1995);

  1. Because paternal mitochondria is so highly mutational, combining both mutating structure and a more stable one in one cell or tissue would result in great damage to the organism:
Join now!
  • If both paternal and maternal mtDNA are present in the cell, it would be a lethal combination due to numerous mutations (Ankel-Simons, Cummins, 1996; Brandon et. al 2005; Danan, 1999; Foley, 2003; Hayashida et al, 2005; Kunchithapadam, 1995; Whittle, Jonston, 2002);
  • If one tissue has maternally inherited mtDNA and another one shows paternal mtDNA in a normal organism (not a hybrid), it could cause:
  1. Failure of T- and B-cells’ recognition of specific tissues;
  2. Increased mutation rate, different for all the tissues of the organism;
  3. Different ATP production. ATP coming from paternally inherited mtDNA may not ...

This is a preview of the whole essay