Genetics 12
mitochondrial genome apis melllifera
mtDNA - gene sequence

Unlike nuclear DNA, which undergoes recombination from generation to generation, mitochondrial DNA only undergoes recombination with DNA from the same organelle, greatly limiting genetic change. Therefore, the only factor that introduces genetic changes is mutation, rather than mutation plus recombination, as is the case with nuclear DNA. This makes mitochondrial DNA into a highly useful genetic marker that can be used to compare different queen lineages.

Mitochondrial DNA is found in the loop format, just like the DNA found in bacteria unlike nuclear DNA, which consists of linear DNA . The genes in the mitochondria express proteins that help build the mitochondria, though over billions of years of evolution, the nuclear DNA has taken up much of the roles of mitochondrial DNA in constructing the mitochondria.

Whereas nuclear DNA consist of over 3 billion base-pairs and codes for over 20 00 proteins, mtDNA is much smaller and in the case of A. mellifera contains 16343 base-pairs consisting of only 37 genes: 2 ribosomal RNA genes, 22 transfer RNA genes, and 13 protein-encoding genes.
The mitochondrial genome for A.mellifera.L was first sequenced in 1992 by R.H. Crozier and Y.C. Crozier. The diagram on the left was adapted from this article but is colour coded to illustrate the various coding regions.
By way of interest the mitochondrial genome of A. cerana was sequenced in 2011by H-W Tan et al.
It was found that the order and orientation of the gene arrangement pattern for A. cerana was identical to that of A. mellifera, except for the position of the tRNA-Ser(AGN) gene shown as S1 in the diagram (top left).
A. mellifera: gene sequence is E S1 M Q A I
A. cerana: gene sequence is S1 E M Q A I
Mitochondrial DNA - mtDNA
structure eukaryotic cell
mtDNA and bee genetics

mtDNA is a valuable tool in the study of bee genetics and the construction of phylogenetic trees either at the species or sub-species level. mtDNA is passed unchanged from generation to generation only along the maternal line i.e. without recombination as with nDNA. This makes it suited to the study of bee genetics for two reasons:
Firstly because all the bees in the colony are the progeny of the queen their mtDNA is identical. This holds when a new queen might be present in the colony after the old queen has swarmed or the old queen is superceded.
Secondly the spread of the bees by swarming to a new area ensures that the mtDNA is identical within the old and new colony.
mtDNA markers - some early results

mtDNA markers have been widely used to study genetic variation within Apis mellifera.
Some early research papers had the objective of finding evidence for the existence of the 4 branches of A. mellifera which Ruttner had proposed in 1984 i.e. M, C, O, and A.

For example in 1991 JM Cornuet and L Garnery used mtDNA to find evidence of the phylogenetic tree of the 4 honeybee species, and further to find evidence of the relationship between the A, M, and C lineages. It is perhaps significant that in this paper no evidence of the existence of the O Group was found.

However in 2000 a paper by P Franck et al which examined colonies from the Lebanon were found to shown mitochondrial patterns different from the A, M, and C lineages. This was thought to provide evidence of the existence of the O Group lineage.
However, new data has shown that this lineage is a sublineage of the A group, and was renamed Z (Alburaki et al. 2011).
The diagram shows the structure of a eukaryotic cell in some detail although still somewhat simplified.

The diagram has been adapted from cellimagelibrary.org where the structure of a cell might be explored more fully.

The two main parts of interest are:
(i) the nucleus and (ii) the mitochondria.

The nucleus contains the chromosomes which only become visible during cell division. The chromosomes define the cell's genotype.

Mitochondrial DNA are small loops of double stranded DNA found within organelles in the cell - the mitochondria. The mitochondria supply most of the energy for nearly all the cells in the body. Most of the energy in nutrients is utilized inside the mitochondria by oxidation to form the ATP molecule that can be used everywhere in the cell as an all-purpose energy supplier. The mitochondria are believed to be the descendants of ancient bacteria that participated so symbiotically with ancient cells that they became integrated into them as organelles
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