Mitochondrial genes are inherited solely from the mother, unlike nuclear genes which are inherited from both parents equally. Mitochondria contain 37 genes that are essential for mitochondrial function. Mitochondrial DNA mutates faster than nuclear DNA due to fewer repair mechanisms and exposure to free radicals during energy production. Mitochondrial DNA is also inherited differently, with mutations able to exist across different mitochondria within the same cell.

1. MITOCHONDRIAL GENES
Ikram Ullah
M.Phil MLSc

2. Mitochondrial Gene
• The basis of the law of segregation, that both parents
contribute genes equally to offspring, does not apply for
genes in mitochondria
• The thousands of mitochondria in each human cell
contain several copies of a “mini-chromosome” that
carries just 37 genes.
• mtDNA-encoded genes act in the mitochondrion, but the
organelle also requires the activities of certain genes from
the nucleus

4. Inheritance Pattern and Mutations
• The inheritance patterns and mutation rates for
mitochondrial genes differ from those for genes in the
nucleus
• Mitochondrial genes are maternally inherited. They are
passed only from an individual’s mother
• Because sperm almost never contribute mitochondria
when they fertilize an oocyte.
• In the rare instances when mitochondria from sperm enter
an oocyte, they are usually selectively destroyed early in
development

6. • DNA in the mitochondria differs functionally from DNA in the
nucleus in several ways Mitochondrial DNA does not cross
over.
• It mutates faster than DNA in the nucleus for two reasons:
• it has fewer ways to repair DNA and the mitochondrion is the
site of energy reactions that produce oxygen free radicals that
damage DNA.
• Also unlike nuclear DNA, mtDNA is not wrapped in proteins,
nor are genes “interrupted” by DNA sequences that do not
encode protein.
• Finally, a cell has one nucleus but many mitochondria—and
each mitochondrion harbors several copies of its chromosome.
• Mitochondria with different alleles for the same gene can reside
in the same cell