Lecture 14 Flashcards
Pseudoautosomal region
Regions of X Y chromosome that match. Line up during meiotic recombination
X-linked recessive
- more severe in male
- skipped generations
- no male to male transmission
- daughters of affected father are carriers
Recurrence risk for X-linked recessive if mother is carrier
Daughter: 50% carrier, 50% normal
Son: 50% affected, 50% normal
6 x-linked recessive disorders
-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
X-linked dominant 4
- predominantly female
- no male to male
- affected male transmits to all his daughters
- variable expressivity
Y-linked disease 3
- mutations in the SRY genes
- H-Y histocompatibility antigen
- hairy ears
Reduced penetrance
Same as incomplete dominance, may complicate an autosomal dominant
Locus heterogeneity 5 diseases
- 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)
Variable expression reasons 3
Random chance
Other genetic factors or sex influence
Environmental exposure
Variable expression diseases 4
Hemochromatosis (AR)
Xeroderma pigmentosum (AR)
CF (AR)
Embryonic development disorder
Germline mosaicism
Mutant sperm in testis
Pleitropy
A disease causing mutation affects multiple organ systems
- Marfan syndrome (AD)
- osteogenesis imperfecta
Delayed age of onset 3
Huntington disease (AD)
Hemochromatosis
Familial breast cancer (BRCA-1 or BRCA-2 mutation)