This might seems a bit basic, but this is how i used to do it
First i would just look at the pedigree and kinda workout what type of inheritence it was
This image shows a dominant autosomal condition
The indications are:
- Males and females affected equally, therefore sex-linked is not indicated
- At least one person in every generation is affected
So now we can workout genotypes based on the information we are given.
Genotypes: (N) disease (n) normal
I-1 Heterozygote (Nn) Has the disease but not all children are affected, therefore he must have one normal gene
I-2 Homozygote (nn) Does not display the disease and since the condition is dominant, must have both normal genes
II-1 Homozygote (nn) Not family, but has no affected children and does not display disease
II-2 Homozygote (nn) Does not display disease
. . . .
You would keep on applying these principles until you worked out the genotype of the required individual. The most important thing you have to do is work out the type of inheritence