Mitochondrial Inheritance
The Circular Chromosome of
the Mitochondrion
A nuclear chromosome is huge and linear.
The mitochondrial chromosome is circular and relatively small.
Mitochondria are Passed from
Mother to Offspring
• In most animals father and mother each
contribute the same number of chromosomes
to the zygote.
• But there are thousands of mitochondria per
egg cell, and only a few in the sperm. And
once the sperm enters the egg, those sperm
mitochondria are usually destroyed.
• The zygote ends up filled with mitochondria
from the egg, therefore the zygote inherits the
maternal mitochondrial DNA.
Because mitochondrial chromosomes
almost never recombine and because
they are inherited so differently,
population bottlenecks lead to a very
rapid loss of mitochondrial diversity.
In this example we begin with four
mothers, each with a different
mitochondrial chromosome.
If each mother has two offspring survive
to maturity, the population is held
constant.
Since only daughters pass on the
mitochondria, mothers who only have
sons end the transmission of that
mitochondrial type.
After only a few generations (in this
example) only one mitochondrial type
remains:
…the mitochondria from Mother #2
Mitochondrial DNA Relationships
Mitochondrial Migrations
Because mitochondrial chromosomes don’t recombine
like nuclear chromosomes, and because they are
maternally inherited, mutations don’t spread laterally
through a population because of mating.
Instead, they are passed, almost clonally, down
through subsequent generations, often becoming
“fixed” when small populations or individuals move to
new areas.
Mitochondrial genetic markers are therefore the best
tools to follow human migrations that have taken place
over the millennia.
Mitochondrial Migrations
Mitochondrial DNA Haplotypes
Source: McDonald Institute for Archaeological Research, University of Cambridge
Mitochondrial DNA
• Eric Lander – Access Excellence
• Argentina - Human Rights
• National Geographic Genographic Project
• Dolan DNA Center - Background on Mitochondrial
DNA
But, mussels are unique among animals!!!
Mytilus has two genetically
different types of mitochondria and
in addition to maternal inheritance
there is also paternal inheritance!!!
More about that in the lab!