Download Nuclear DNA Mitochondrial DNA (mtDNA)

Nuclear DNA v mtDNA:
Principles of inheritance
Nuclear DNA
Mitochondrial DNA (mtDNA)
- Found in the nucleus of the cell
- 3,300,000,000 bases arranged in linear chromosomes
(above)
- Two copies of each chromosome present
- Maternally and paternally inherited
- Contains approximately 20,000
- 30,000 genes
.
- 93% of the genome contains non-coding DNA
-
Mendelian inheritance
Non-Mendelian inheritance
Mother:
‘unaffected’ carrier
Father:
‘unaffected’ carrier
Found in the mitochondrial matrix
16,569 bases in a circular chain of DNA
Multiple copies present in each mitochondrion
Maternally inherited
Contains 37 genes that encode
- 13 proteins
- 22 tRNAs and 2 rRNAs
- 3% of the genome contains non-coding DNA
= Cell nucleus
‘Mother’ cell
containing
mutant
mtDNA
= Normal
mitochondria
= Mutant
mitochondria
Primary
oocytes
mtDNA
amplification
‘unaffected’ child:
1 in 4 chance
‘unaffected’ carrier child:
2 in 4 chance
‘affected’ child:
1 in 4 chance
- This example represents an autosomal recessive disease
- Both parents have one ‘healthy’ gene, and one ‘disease’
gene; as the ‘healthy’ gene over-rides the ‘disease’ gene,
the parents are healthy
- There is a ¼ chance that their children will carry two
copies of the ‘healthy’ gene, a ½ chance their children will
carry one copy of the ‘healthy’ gene, and one copy of the
‘disease’ gene, and will be healthy like the parents, and ¼
chance they will inherit two copies of the ‘disease’ gene. In
this case, the child will inherit the disease
Mature
oocytes
Fertilisation
Low level of
mutation:
Healthy child
Intermediate level
of mutation:
Mild disease
High level of
mutation:
Severe disease
- The mother may have a mixed population of mitochondria
that contain ‘normal’ mtDNA and ‘mutated’ mtDNA that
causes disease; this is called heteroplasmy
- If heteroplasmy is present in pre-cursor egg cells, the
daughter egg cells may have mitochondria containing a
differing contribution of ‘healthy’ and mutated mtDNA
- One factor in the severity of disease is the proportion of
‘normal’ mtDNA in relation to ‘mutated’ mtDNA; the more
mutated mtDNA, the worse the disease