Genetics
AKT High-Yield Breakdown
Genetics in primary care focuses on recognising heritable conditions, understanding inheritance patterns, interpreting pedigrees, and counselling patients appropriately. The AKT tests classical inheritance patterns, the clinical features that distinguish common genetic syndromes, chromosomal disorders, and the principles of pre- and post-test genetic counselling.
What You'll Learn
Master autosomal dominant and recessive inheritance calculations, X-linked condition sex distributions, the distinguishing features of Down's/Turner's/Klinefelter's syndromes, BRCA1/2 referral criteria, trinucleotide repeat disorders, and the principles of non-directive genetic counselling.
Practise Genetics MCQs
From inheritance patterns and chromosomal disorders to BRCA1/2 referral criteria, pharmacogenomics (CYP2D6, HLA-B*5701, TPMT), and the distinction between dominant and recessive conditions — tackle focused MCQs across the full Genetics curriculum.
Inheritance Patterns
Understanding inheritance patterns allows prediction of risk to offspring and identification of at-risk family members. These appear frequently as pedigree interpretation questions in the AKT.
Autosomal Dominant (AD)
- Affects males and females equally; every generation affected (vertical transmission); affected individual has 50% chance of passing to each child
- New mutations common (de novo): no family history does not exclude AD; look for this pattern in Achondroplasia, Marfan syndrome (advanced paternal age → increased mutation rate)
- Variable expressivity: same mutation → different severity between family members (e.g. NF1)
- Reduced penetrance: mutation present but not expressed (e.g. BRCA2 — not all carriers develop cancer)
- Examples: Huntington's disease, NF1/NF2, Marfan syndrome, familial hypercholesterolaemia, ADPKD, Myotonic dystrophy (anticipation — worsens across generations), BRCA1/2
Autosomal Recessive (AR)
- Affects males and females equally; typically skips generations; two carrier parents → 25% affected, 50% carrier, 25% unaffected
- Consanguinity increases risk (common ancestors increase likelihood of both parents being carriers)
- Carrier frequency: Hardy-Weinberg equilibrium; if disease frequency 1/2500, then carrier frequency = 1/25 (q² = 1/2500; 2pq ≈ 2q = 1/25)
- Examples: cystic fibrosis, sickle cell disease, thalassaemia, haemochromatosis, PKU (phenylketonuria), Wilson's disease, glycogen storage diseases, congenital adrenal hyperplasia
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