By Loren Bolinger, November 23, 2007

http://www.mitotyper.com - the place where you can find answers to many of your questions about maternal inheritance.

The mitochondria exist in the cytoplasm of the ovum [the white of the egg], which is located outside of the nucleus of the cell. They contain non- or extra-nuclear DNA. The mitochondrial genome is replicated from the dam to her offspring, both sons and daughters, but only the daughters can, in turn, pass the mitochondrial genome to their offspring. Maternal inheritance through mitochondrial DNA occurs in all mammals.

Since sperm essentially have no cytoplasm [as used in reproduction], mitochondria inherited from his mother cannot be replicated from the son to his offspring. This means that mitochondrial DNA is only passed through matrilineal descent from the founder mare of a female family to her descendants.

The mitochondrial genome is unusual in the sense that it does not split and recombine as happens with the Mendelian [nuclear] genomes. Instead, it is replicated or cloned from mother to daughter. Barring mutation, genetic disease, or the occasional SNP (single-nucleotide polymorphism), the mitochondrial genome of today's descendant of a female family is identical to that of the founder mare of that family, some 300 to 400 years ago.

In this sense, the unchanging mitochondrial genome is ancient DNA, since nuclear DNA is recreated in new and unique combinations in each individual. The ancient maternal-DNA interacts with a new nuclear genome every time a new foal is created.  A genetic gift from the founder matriarch reaches forward in time to touch and bless each of her descendants.

There are 37 genes in the mitochondrial genome [13 for proteins (polypeptides), 22 for transfer RNA (tRNA) and one each for the small and large subunits of ribosomal RNA (rRNA)]. Many are involved with the creation, conversion, and regulation of Adenosine Triphosphate, the fuel of the cell and so therefore, the creature made from those cells. These maternal genes work in close association with the genes in the nuclear genome, independently, cooperatively, and are intimately linked with each other.

In contrast to the nuclear genome which is linear, right-handed, and double-helix in construction, the mitochondrial genome is circular. It is composed of 16,596 bp (Equus Caballus complete mitochondrial genome available at: http://www.ebi.ac.uk/) or 16,660 bp( http://megasun.bch.umontreal.ca/ogmp/projects/other/genbank/MIECCOMP.txt ).  Its DNA is composed of combinations of adenine (A), guanine (G), cytosine (C), and thymine (T) and does not recombine. It is made of the same material as nuclear DNA but is independent and its mechanisms operate in completely different fashion.

The great Australian horseman, Charles Bruce Lowe, was the first horseman to recognize, popularize, and write about the importance of maternal inheritance. He made his discovery solely through the powers of observation and his intellect, without the benefit of laboratory or microscope.

- Loren Bolinger, November 23, 2007