Genetics Flashcards
A woman’s previous son has Duchenne muscular dystrophy. What is the chance that her current fetus is affected? a - 0% b - 10% c - 25% d - 33% e - 50%
c - 25%
X-linked recessive
What percentage of patients are negative for HpA1a antigen?
A - 0.0002% B - 0.02% C - 0.2% D - 2% E - 20%
D - 2%
Majority of people are HPA 1a for platelets
Cause of alloimmune thrombocytopenia
A man has an X-linked disorder and his wife is homozygous normal. What is the chance that their two children will both be affected?
a - 0 b - 1/16 c - 1/8 d - 1/4 e - 1/2
a - 0
0% if x-linked recessive
50% if x-linked dominant for each baby
- therefore 25% that both will be affected
O
All of the following patterns of inheritance are correct except:
A - von Recklinghausen’s – autosomal dominant
B - Huntington’s chorea – autosomal dominant
C- Cystic fibrosis – autosomal recessive
D - Tay Sach’s – autosomal dominant
D - Tay Sach’s – autosomal dominant
Autosomal recessive
von Recklinghausen’s – autosomal dominant, neurofibromatosis type 1
Klinefelters syndrome characteristics include all of the following except:
A - testicular hypoplasia B - raised serum FSH level C - azoospermia D - low levels of testosterone E - impotence
E - impotence
O
The husband of a normal female has Christmas disease. She gave birth to a son. What is the probability that he is affected?
A - none B - 10% C - 25% D - 33% E - 50%
A - none
Christmas disease = haemophilia B
X-linked recessive
Therefore if the husband has the disorder there is no chance a son will have it given that the Y is inherited from the father. A daughter would be a carrier.
An adopted woman has recently been informed that her natural mother died from Huntington’s chorea. What is the risk that her unborn child is affected?
A - 50% B - 25% C - none D - none if the baby is male E - none if the baby is female
B - 25%
Milford
50% chance she is affected and if so 50% chance of passing down -> 25%
Which of the following conditions is autosomal recessive?
A - Haemophilia A B - Cystic fibrosis C - Tuberous sclerosis D - Huntington’s chorea E - Adult polycystic kidney disease F - Marfan's syndrome G - Multiple sclerosis
B - Cystic fibrosis
O
tuberous sclerosis - rare, autosomal dominant, benign tumours in kidneys, liver, heart, lung, eyes
Which of the following tests is most useful in diagnosing haemoglobinopathy?
A - HbEPG B - Bone marrow C - DNA analysis D - Red cell index E - Blood film
A - HbEPG
HbEPG - haemboglobin electrophoresis, this checks for HbS carrier status, thalassaemia
Doesn’t help a diagnosis of Alpha thal?
One partner of a couple with recurrent miscarriage has a balanced reciprocal translocation – the most correct is:
A - phenotypically normal offspring in 50% of conceptions
B - major anomalies with trisomy in 25%
phenotypically normal in 10% if husband has translocation
C - phenotypically normal in 70% if mother has translocation
D - all offspring will have a balanced translocation
A - phenotypically normal offspring in 50% of conceptions
Fragile X syndrome
A - occurs only in men B - Mendelian inheritance C - associated with premature menopause D - no phenotypic features E - none of the above
C - associated with premature menopause
Fragile X syndrome has traditionally been considered an X-linked recessive condition with variable expressivity and possibly reduced penetrance. However, due to genetic anticipation and X-inactivation in females, the inheritance of Fragile X syndrome does not follow the usual pattern of X-linked dominant inheritance, and some scholars have suggested discontinuing labeling X-linked disorders as dominant or recessive. Females with full FMR1 mutations may have a milder phenotype than males due to variability in X-inactivation.
FMR1 Mutation. Trinucleotide expansion repeat - more repeats = more severe disease. Can have pre-mutation which contributes to POI.
Which chromosomal abnormality doesn’t increase in frequency with increased maternal age?
A - Trisomy 21
B - Trisomy 18
C - Turners XO
D - XXY
C - Turners XO
Milford
Klinefelters – advice to pregnant woman about likely phenotype. Which is not a feature?
A - gynaecomastia B - female fat distribution C - serious mental retardation D- infertility E - tall eunuchoid habitus
C - serious mental retardation
only mild intellectual disability
Which of the following genetic conditions is NOT associated with a particular ethnic group or groups?
A. Tay-Sachs disease
B. von Willebrand disease
C. Sickle cell disease
D. Alpha thalassaemia
B. von Willebrand disease
O
Which of the following would NOT be an accurate description of 47XXY in an adult?
A. serious intellectual disability
B. tall stature
C. elevated Serum FSH
D. female fat distribution
A
Klinfelters - Mild intellectual disability usually
