Only one copy required to cause disease, disease seen in all generations
A person affected by an autosomal dominant disorder has a 50% chance of passing the mutated gene to each child
Recessive
2 copies of faulty gene required to cause disease, often only 1 generation affected
1 in 4 risk of child being affected if parents are carriers
X linked inheritance
Gene fault lies on X chromosome
X-linked recessive inheritance - a female with one pathogenic allele and one normal allele does not show major clinical features of the disease, but a male with a single faulty allele will be fully affected
Carrier female may have an unaffected son (1/4), affected son (1/4), unaffected daughter (1/4), carrier daughter (1/4)
If an affected male has children, all his daughters will be carriers and all his sons will be unaffected (no male-male transmission)
Female carrier may show mild features – X inactivation (around ½ of cells will have faulty gene)
Mitochondrial inheritance
The mitochondria in the cell have their own genome (single loop)
In many cases, a mutation in the mitochondrial genome is only present in a proportion of the mitochondria, and the proportion varies between cells within an individual
Mitochondrial DNA is transmitted maternally, in the ovum
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