Lecture 16

Question 1

Key words

Answer 1

Dominant - Vertical patterns of affected individuals
Recessive - Horizontal patterns of affected individuals
Autosomal recessive - Consanguinity often present between parents
Autosomal - Males and females affected with equal probability
X-linked recessive - Males affected, female carriers
X-linked dominant - All daughters of affected males are affected
Mitochondrial - Non-Mendelian, Maternal inheritance

Question 2

Autosomal dominant

Answer 2

Every affected individual has an affected biological parent
•Males and females equally likely to be affected
•Recurrence risk of each child of an affected parent is 50%
•Normal siblings do not transmit the trait to their offspring

Question 3

Autosomal recessive

Answer 3

Males and females equally likely to be affected
•Recurrence risk of each child of an affected parent is 25%
•Trait is characteristically found in siblings, not parents
•Parents of affected children may be related (consanguineous mating)
•Trait may appear as an isolated (sporadic) event

Question 4

X linked recessive

Answer 4

• Males are much more likely to be affected than females
• Trait is never passed from father to son
• All affected males in a family are related through their mothers
• Passed from an affected grandfather, through his carrier daughters, to half of his grandsons

Question 5

Mitochondrial

Answer 5

• Non-Mendelian

* Everyone inherits the condition through the maternal line

Question 6

Complications that affect interpretation of pedigrees

Answer 6

1. New mutations
2. Penetrance
3. Expressivity
4. Delayed onset
5. Anticipation
6. Imprinting

Question 7

Molecular markers allow mapping:

Answer 7

Phenotypic markers e.g. genetic disorder
•Molecular markers e.g.
–Structural rearrangements
–SNPs
–RFLPs
–INDELS
–Copy number variations eg VNTRs with multiple alleles

Question 8

Statistical analysis

Answer 8

lod score = log10 odds loci are linked odds loci are unlinked
•lod scores are logarithms, so data from separate families can be pooled from different pedigrees by adding lod scores
•lod score ≥ 3.0 indicates likelihood of observing the given pedigrees if the two loci are not linked is less than 1 in 1000