Genetic Disorders (18)

Question 1

How are males represented on pedigree diagrams?

Answer 1

square

Question 2

How are females represented on pedigree diagrams?

Answer 2

circle

Question 3

How are affected individuals represented on pedigree diagrams?

Answer 3

black square/circle

Question 4

How are carriers of autosomal disorders represented on pedigree diagrams?

Answer 4

half black half white square/circle

Question 5

How are (female) carriers of X-linked disorders represented on pedigree diagrams?

Answer 5

filled circle w/in white circle

Question 6

How are deceased people shown on pedigree diagrams?

Answer 6

line through them

Question 7

How are probands shown on pedigree diagrams (person consulting you)?

Answer 7

arrow pointing to square/circle

Question 8

How are couples represented on pedigree diagrams?

Answer 8

linked by horizontal line

Question 9

How are offspring represented on pedigree diagrams?

Answer 9

linked to parents by vertical line

Question 10

How are dizygotic and monozygotic twins represented on pedigree diagrams?

Answer 10

dizygotic: two lines in a triangle shape
monozygotic: two lines with a small triangle above

Question 11

How are consanguineous matings shows on pedigree diagrams?

Answer 11

linked by double line

consanguineous if 2nd cousins or closer
2nd cousins share 3.13% DNA

Question 12

Why do we draw pedigree diagrams?

Answer 12

• provides a clear, simple summary of info
• able to spot patterns easily
• explain pattern to patient
• calculate risk of passing on disease or being a carrier
• allows informed choice

Question 13

What are complicating factors with pedigree diagrams?

Answer 13

• age of onset e.g. Huntington’s
• -> someone may die before developing disease–> hole in pedigree

N.B. more repeats means more severe disease

Question 14

What are complicating factors with mitochondrial inheritance?

Answer 14

• offspring inherit different numbers of mutated mitochondria from mother
• different tissues/cells can contain different numbers and this can change with time
• some diseases develop w/ age due to accumulation of mutated mitochondria

Question 15

What could a sporadic inheritance pattern indicate?

Answer 15

• non-genetic disorder

- chromosomal abnormality

Question 16

What is risk?

Answer 16

a calculation of the predicted chance of having the disease or being a carrier

Question 17

How do we calculate risk?

Answer 17

• work from person with known phenotype
• multiply risks together
• take account of all information: phenotype, disease characteristics (e.g. age of onset), and family distribution (e.g. mitochondrial)
• consider ethnic background e.g. sickle cell

Question 18

If a couple who are known to both be carriers of a recessive disease have an unaffected child- what is the risk of their child being a carrier?

Answer 18

2/3 as we know child is unaffected so we remove 1 possibility

(Bayesian statistics)

Question 19

If a woman whose paternal uncle has an X-linked recessive disease, what is the risk of her having an affected son?

Answer 19

population risk bc her father is not affected and no one affected in maternal family