Genes and BioTechnologyPedigrees are a little like family trees.
The big difference is that a pedigree is used to display the inheritance of a particular trait; eg., blue eyes and blond hair in a family or more importantly inherited (or congenital) diseases that are passed from one family member to another.
Symbols used on Pedigrees
Autosomal Recessive Inheritance
For an individual to express an autosomal recessive trait both copies of the allele must be present
If both parents affected then all offspring will also be affected.
Recessive traits tend to skip generations with few individuals affected.
Autosomal Dominant Inheritance
For an autosomal dominant trait to be expressed only one copy of the allele is required.
Usually present in each generation, many affected individuals.
If the homozygous dominant condition is lethal the phenotypic and genotypic ratios will be different.
X-linked Recessive Inheritance
Males only require one allele to express the trait, therefore more males than females will show the trait.
Females require both alleles to show the trait.
Heterozygous females are described as carriers of the trait
X-linked dominant inheritance
Any individual with the trait must have a parent with the trait
Females may be heterozygous and show the trait
This condition is much harder to detect.