Pedigrees and Risk Assessment

Question 1

Describe the Autosomal Dominant inheritance pattern.

Answer 1

affected individuals have usually have one affected parent
affects both sexes equally
vertical transmission (phenotype seen in multiple generations)
50% recurrence risk

Question 2

Describe the Autosomal Recessive inheritance pattern.

Answer 2

affected individuals usually born to unaffected carrier parent
affects both sexes equally
horizontal transmission (seen in siblings but not other generations)
25% recurrence risk

Question 3

Describe the X-linked Penetrant in Females (X-linked dominate) inheritance pattern.

Answer 3

usually at least one parent affected
phenotype in affected females is milder and more variable than affected males
affects either sex but not equally (more males than females- almost 2X)
affected mothers- 50% chance of affectedness in either sex
affected fathers- all daughters affected, all sons unaffected non-carriers
vertical transmission

Question 4

Describe the X-linked Females Unaffected (X-linked recessive) inheritance pattern.

Answer 4

parents of unaffected males are usually unaffected- mother normally asymptomatic carrier
females may be affected if father is affected and mother carries OR due to non-random X-inactivation
affects mainly males
vertical transmission with “skipped generations”
NO male-to-male transmission
carrier mother- 50% affected sons, 50% unaffected carrier daughters
affected father- all sons non-carriers, all daughters unaffected carriers
can mimic recessive pedigree

Question 5

Describe the Y-linked inheritance pattern.

Answer 5

affected males almost always have an affected father
affects only males
vertical transmission
all sons of an affected father are affected

Question 6

What inheritance patterns are Mendelian?

Answer 6

AR
AD
X-linked Female Affected
X-linked Female Unaffected
Y-linked

Question 7

What inheritance patterns are non-Mendelian?

Answer 7

mitochondrial
imprinting
multifactorial

Question 8

Describe the Mitochondrial inheritance pattern.

Answer 8

IF the disorder is 100% penetrant, then all children of an affected mother will be affected
affects both sexes equally
vertical transmission
exclusively inherited via maternal line
can mimic AD pedigree

Question 9

Describe the inheritance of imprinting.

Answer 9

the epigenetic phenomena by which certain genes are expressed in a parent-of-origin specific manner with the phenotype depending on which parent passes on the gene
will mimic AD with variable expressivity

Question 10

Describe a multifactorial inheritance pattern.

Answer 10

condition caused by a combination of genetic and environmental factors
no characteristic inheritance pattern

Question 11

What factors contribute to the recurrence risk of a multifactorial condition?

Answer 11

if proband is severely affected, the risk to close relatives is greater
risk is greater among close relatives and decreases with distance of relationship
more than one affected family member increases risk to other relatives
if disorder is more common in one sex and the opposite sex is affected then recurrence risk is greater for relatives

Question 12

What is the coefficient of relationship?

Answer 12

R

the proportion of genes that two people share by virtue of their relationships

Question 13

What is the coefficient of inbreeding?

Answer 13

F
measure of the level of consanguinity
probability that a child of a consanguineous marriage will be homozygous for a specific gene derived from a common ancestor
OR
the proportion of loci at which a person is homozygous by decent