1. Pedigrees
A Pedigree allows you to trace an inherited (genetic) disease through a family.
The pattern of a pedigree helps determine:
If the disease is inherited
If the disease is dominant or recessive
Pedigrees use standardized symbols

2. Sickle Cell Disease Pedigree

3. Translating family information into pedigrees
A girl with a genetic disease has 2 sisters and one brother. Her brother has the same disease, but her sisters do not. Her mother has the disease but her father does not.
Draw pedigree here:

4. Dominant or recessive? Copy these pedigrees into your notes
For each case, determine whether the disease is dominant or recessive
Assign genotypes for each individual
Case #1
Case #2
Case #3

5. “Guess and check”- Case #1
If the disease is DOMINANT:
All individuals without the disease must be homozygous recessive.
All individuals with the disease must have at least one dominant allele (they are either homozygous dominant, or they are heterozygous) aa aa aa aa
A ?
Is this possible?
NO, the person with the disease could not inherit a dominant “A” if both parents have only “aa” genotypes.

6. “Guess and check”- Case #1
If the disease is RECESSIVE:
All individuals with the disease must be homozygous recessive.
All individuals without the disease must have at least one dominant allele (they are either homozygous dominant, or they are heterozygous)
A ? a
A ? a aa
A ?
A ?
Is this possible?
YES, the person with the disease could inherit a recessive “a” if both parents are heterozygous “Aa”
Therefore, this pedigree shows a recessive disease.

7. Case #2- Dominant or recessive?
Try dominant disease alleles:
Try recessive disease alleles:
Is dominant possible?
Is recessive possible?

8. Case #3- Dominant or recessive?
Try dominant disease alleles:
Try recessive disease alleles:
Is dominant possible?
Is recessive possible?