Lecture 17

Question 1

mitochondrial inheritance as seen on a pedigree?

Answer 1

1. all offspring of affected female are affected
2. only females transmit the disease
3. can occur in both genders

Question 2

Explain heteroplasmy?

Answer 2

The severity of the disorder depends on the number of mitochondria that have the mutant gene

explains variable expression

Question 3

Examples of mitochondrial diseases

Answer 3

1. Leber hereditary optic neuropathy
2. MELAS
3. MERRF

Question 4

example of a digenic disorder?

Answer 4

Retinitis pigmentosa

Question 5

Imprinting disorders

Answer 5

Prader Willi syndrome

Angelman syndrome

Question 6

Triplet repeat disorders

Answer 6

Huntington disease (autosomal dominant) 
Myotonic dystrophy (autosomal dominant)
Fragile X syndrome (X-linked)

Question 7

How do digenic disorders occur?

Answer 7

Mutations in two genes (A, B) are additive and necessary to produce the disorder

Question 8

retinitis pigmentosa

Answer 8

digenic disorder

progressive visual impairment
a result of a mutation in two independent genetic loci (ROM1 and peripherin)
Heterozygotes for gene A and gene B have retinitis pigmentosa

Question 9

Prader- willi syndrome

Answer 9

microdeletion of paternal chromosome 15

microdeletion of the paternal SNRPN gene

no active copy of the SNRPN gene (maternal copy is silenced)..but has two active copies of the UBE3A gene

Question 10

symptoms of prader-willi syndrome

Answer 10

Children are usually obese, have mental and developmental delay and underdeveloped genitalia

Question 11

how can methylated DNA be analyzed?

Answer 11

southern blot

PCR and DNA sequencing

Question 12

angelman syndrome

Answer 12

deletion of the maternal gene UBE3A

two copies of the SNRPN gene and no UBE3A gene functioning

Question 13

symptoms of angelman syndrome

Answer 13

Severe intellectual disability
seizures
Puppet like posture of limbs

Question 14

What basepairs are repeated in fragile X syndrome

Answer 14

CGG

Question 15

What basepairs are repeated in Friedrich ataxia

Answer 15

GAA

Question 16

What basepairs are repeated in HD

Answer 16

CAG

Question 17

What basepairs are repeated in Myotonic

dystrophy

Answer 17

CTG

Question 18

What is anticipation?

Answer 18

The larger the repeat, the greater is the chance for it to be unstable and it tends to expand from one generation to the next

Question 19

What diseases are anticipation found?

Answer 19

1. HD
2. myotonic dystrophy
3. Fragile X syndrome

Question 20

What gene mutation leads to fragile X syndrome

Answer 20

FMR1

Question 21

symptoms of fragile X syndrome

Answer 21

Intellectual disability
learning difficulties
prominent ears
elongated face
macro orchidism

females are less impacted
shows anticipation
more repeats = increased severity

Question 22

Fragile X syndrome diagnostic test

Answer 22

southern blot analysis