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
Crossing over of chromosomes occurs during:
A. metaphase I. B. mitotic prophase. C. meiotic prophase I. D. meiotic prophase II. E. both mitotic and meiotic prophase.
C. meiotic prophase I.
O
Which of the following disorders is NOT usually considered autosomal dominant?
a) Achondroplasia
b) Huntington’s Disease
c) Myotonic Dystrophy
d) Thanataphoric Dwarfism
e) Tuberous Sclerosis
d)
As per RANZCOG MCQs August 2008
“NOT usually”
Both are inherited by autosomal dominance BUT most of the time are due to a denovo mutation so majority of cases are not attributed to inhertiance.
Thanataophoric dwarfism almost all cases are denovo and are lethal most of the time.
Achondroplasia - FGFR3 mutation - heterozygote
Thanataphoric Dwarfism - FGFR3 mutation - homozygote
Which inherited genetic condition is most common?
a. Cystic Fibrosis
b. Duchenne Muscular dystrophy
c. Tay - Sachs
d. Phenylketonuria
e. Huntington’s disease
a. Cystic Fibrosis
O
Affects 1:2000 livebirths
DMD - X recessive 1:3600 boys
PKU - Autosomal recessive 1:13500-19000
TS - Autosomal recessive 1:25-30 Ashkenazi jews and 1:3600 other populations
Which congenital anaemia is inherited as autosomal dominant and found in people of European descent?
a. Pyruvate Kinase deficiency
b. Glucose 6 Phosphate dehydrogenose deficiency
c. Hereditary spherocytosis
d. Sickle Cell anaemia
c. Hereditary spherocytosis
- autosomal recessive or autosomal dominant
- most common in Northern European and Japanese families
- related to membrane proteins in red cells
- can cause haemolytic anaemia
Pyruvate Kinase deficiency
- autosomal recessive
Glucose 6 Phosphate dehydrogenose deficiency
- X-linked recessive disorder
Sickle Cell anaemia
- autosomal recessive
Which of the following disorders does NOT have autosomal dominant inheritance?
a. Huntington’s chorea
b. Von Recklinghausen’s disease (neurofibromatosis)
c. Achondroplasia
d. Tay-Sachs disease
d. Tay-Sachs disease - autosomal recessive
Which type of inheritance is wrong?
A. Duchenne muscular dystrophy – autosomal recessive
B. Tuberous sclerosis – autosomal dominant
C. Myotonic dystrophy – autosomal dominant
D. Tay Sach’s disease – autosomal recessive
A. Duchenne muscular dystrophy – autosomal recessive
M
Is X-linked recessive
Down’s syndrome is associated with all except
A. Long femur and humerus B. Duodenal atresia C. Increased nuchal thickness D. VSD E. Ear abnormalities
A. Long femur and humerus
M
Cystic fibrosis is inherited by which mode of inheritance?
A. autosomal dominant B. autosomal recessive C. sex-linked dominant D. sex-linked recessive E. polygenic
B. autosomal recessive
O
