Lecture 14

Question 1

Pseudoautosomal region

Answer 1

Regions of X Y chromosome that match. Line up during meiotic recombination

Question 2

X-linked recessive

Answer 2

• more severe in male
• skipped generations
• no male to male transmission
• daughters of affected father are carriers

Question 3

Recurrence risk for X-linked recessive if mother is carrier

Answer 3

Daughter: 50% carrier, 50% normal
Son: 50% affected, 50% normal

Question 4

6 x-linked recessive disorders

Answer 4

-dystrophin associated muscular dystrophy
    DMD
    Becker muscular dystrophy
-G6PD deficiency
-Hemophilia A and B
-Lesch-Nyhan syndrome (HGPRT deficiency)
-Red-green color blindness
-x-linked SCID

Question 5

X-linked dominant 4

Answer 5

• predominantly female
• no male to male
• affected male transmits to all his daughters
• variable expressivity

Question 6

Y-linked disease 3

Answer 6

• mutations in the SRY genes
• H-Y histocompatibility antigen
• hairy ears

Question 7

Reduced penetrance

Answer 7

Same as incomplete dominance, may complicate an autosomal dominant

Question 8

Locus heterogeneity 5 diseases

Answer 8

• osteogenesis imperfecta: defect in collagen, mutations of chromosome 17 or chromosome 7
• sensorineural hearing impairment
• retinitis pigmentosa
• Charcot Marie Tooth disease (AD, AR, x-linked)
• SCID (AR, x-linked)

Question 9

Variable expression reasons 3

Answer 9

Random chance
Other genetic factors or sex influence
Environmental exposure

Question 10

Variable expression diseases 4

Answer 10

Hemochromatosis (AR)
Xeroderma pigmentosum (AR)
CF (AR)
Embryonic development disorder

Question 11

Germline mosaicism

Answer 11

Mutant sperm in testis

Question 12

Pleitropy

Answer 12

A disease causing mutation affects multiple organ systems

• Marfan syndrome (AD)
• osteogenesis imperfecta

Question 13

Delayed age of onset 3

Answer 13

Huntington disease (AD)
Hemochromatosis
Familial breast cancer (BRCA-1 or BRCA-2 mutation)