image.png
for this image give 3 mark question for spotting
Reading File
Finding Sources
Reading File
Reading File
Here is a complete 3-mark spotting question based on the image:
Spotting Question (3 Marks)
"Identify the given specimen/image and answer the following:"
Image: A karyotype showing 22 pairs of autosomes and a single X chromosome in the sex chromosome position (circled), with the label "XX" indicating only one X is present instead of two.
Q1. What is the diagnosis? Name the karyotype. (1 mark)
Answer:
- Diagnosis: Turner Syndrome (Gonadal Dysgenesis)
- Karyotype: 45, X0 (monosomy X - only one X chromosome, second sex chromosome is absent)
Q2. What is the mechanism of this chromosomal abnormality, and what happens to the ovaries? (1 mark)
Answer:
- The abnormality arises due to non-disjunction during gametogenesis, leading to loss of one X chromosome (most commonly of paternal origin).
- About 50% of cases have a pure 45,X karyotype; 25% show structural abnormalities of the second X; 25% show mosaicism.
- The ovaries undergo accelerated follicular atresia in utero, resulting in streak ovaries (fibrotic, non-functional gonads) - causing primary amenorrhea and hypergonadotropic hypogonadism.
Q3. List any FOUR clinical features (stigmata) of this syndrome. (1 mark)
Answer (any 4 of the following):
- Short stature (most consistent feature)
- Webbed neck (pterygium colli)
- Shield chest with widely spaced nipples
- Cubitus valgus (increased carrying angle of arms)
- Low posterior hairline
- High-arched palate
- Short 4th metacarpal
- Coarctation of the aorta (~30%)
- Horseshoe kidney (renal anomaly)
- Primary amenorrhea / absent secondary sexual characteristics
Bonus/Examiner's note: If a Y cell line is detected on karyotype, gonadectomy is recommended due to increased risk of gonadoblastoma.
(Source: Berek & Novak's Gynecology; Thompson & Thompson Genetics and Genomics in Medicine)
image.png
for this image give 3 mark question for spotting
Finding Sources
Reading File
Finding Sources
Reading File
Here is a complete 3-mark spotting question based on the image:
Spotting Question (3 Marks)
"Identify the given karyotype and answer the following:"
Image: A karyotype showing 22 pairs of autosomes with three copies of chromosome 21 (circled in red) and XY sex chromosomes - indicating a male individual with an extra autosome.
Q1. What is the diagnosis? Write the karyotype. (1 mark)
Answer:
- Diagnosis: Down Syndrome (Trisomy 21)
- Karyotype: 47, XY, +21 (male with an extra chromosome 21)
- Incidence: ~1 in 800 live births
Q2. What is the cytogenetic basis of this condition? Give the three chromosomal types and their frequencies. (1 mark)
Answer:
| Type | Mechanism | Frequency |
|---|---|---|
| Trisomy (free trisomy) | Non-disjunction in maternal meiosis I (>90% maternal origin) | 95% |
| Robertsonian translocation | Extra chr. 21 fused to chr. 13/14/15/21/22; ~1/3 cases have a carrier parent | 4% |
| Mosaicism | Non-disjunction in early mitosis; milder phenotype | 1% |
- Risk increases sharply with advancing maternal age (1:1500 at age 20 → 1:30 at age 45)
Q3. List any FOUR clinical features of Down syndrome AND name ONE serious long-term complication. (1 mark)
Answer - Clinical Features (any 4):
- Hypotonia at birth (most common newborn finding)
- Brachycephaly with flat occiput
- Upward slanting palpebral fissures + epicanthic folds + Brushfield spots
- Protruding tongue and small ears
- Single palmar (simian) crease (present in ~50%)
- Congenital cardiac defects (40-45%) - AV canal defect, VSD, PDA, Tetralogy of Fallot
- Short stature, short neck with excess nuchal skin
- Clinodactyly (curved 5th finger), wide gap between 1st and 2nd toes
Long-term complication:
- Alzheimer's disease in virtually all adults by middle age - due to gene dosage effect of the Amyloid Precursor Protein (APP) gene located on chromosome 21
- Also: increased risk of acute leukemia (especially AML of megakaryocytic type in children <4 years, linked to GATA1 mutation)
(Source: Emery's Elements of Medical Genetics and Genomics; Langman's Medical Embryology; Harrison's Principles of Internal Medicine)
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