Some helpful hints on how to solve pedigree problems

Some rules of thumb to determine the mode of inheritance:

Dominant traits:

Affected individuals have at least one affected offspring.

The phenotype appears every generation.

Unaffected progeny do not transmit the trait to their offspring.

Two unaffected parents have only unaffected offspring.

Recessive traits:

Unaffected parents can have affected offspring.

Affected progeny are both male and female.

May skip generations.

X-linked dominant:

Trait is never passed from father to son.

All daughters of an affected father are affected.

Male phenotype is generally more severe than female phenotype although more females are typically affected.

X-linked recessive:

Trait is never passed from father to son.

Males are more likely than females to be affected.

All affected males in a family are related through their mother.

The above is taken from http://bioserv.fiu.edu/~biolab/labs/genetics/karyotyping%20and%20web%20problems.htm.