Pedigree and risk

Question 1

Why draw a pedigree?

Answer 1

• provides clear simple summary of information
• ability to spot patterns easily
• Can explain pattern to patient
• identify possible carriers of risk gene
• calculate risk of passing on disease or being a carrier

Question 2

What three things should you look for when reading a pedigree?

Answer 2

Who is the condition inherited from: mothers only, fathers only or either?

Can unaffected parents have an affected child? or Can affected parents have an unaffected child?

Is there any sex predilection?

Question 3

What type of inheritance is it if inherited from

• Mothers only?
• Fathers only?
• Either?

Answer 3

Mothers only: Mitochondrial
Fathers only: Y linked
Either: neither - move on to question two

Question 4

What type of genetic inheritance is shown on a pedigree if unaffected parents have an affected child? or affected parents have an unaffected child?

Answer 4

if unaffected parents have an affected child?
Recessive trait - heterozygous parents

If affected parents have an unaffected child?
Dominant trait - heterozygous parents

Question 5

What genetic inheritance is it likely to be if
it is more common in females?
it is more common in males?
no sex predilection?

Answer 5

More common in females: Tends to be X-linked dominant (affected male transmits disease only to the daughters)
More common in males: Tends to be X-linked recessive (affected female transmits disease only to the sons)
No sex predilection: Autosomal inheritan

Question 6

What are the difficulties with drawing a pedigree?

Answer 6

Incomplete information - missing relatives information
Incorrect information
Family history is wrong

Question 7

What is risk?

Answer 7

The predicted chance of having the disease or being a carrier

Question 8

How is risk calculated?

Answer 8

1. figure out pattern of inheritance
2. figure out genotypes
3. calculate probabilities