AN74.1-4 | Patterns of Inheritance — Summary & Reflection

REFLECT

KEY TAKEAWAYS

This guide covered the major patterns of inheritance mandated by NMC competencies AN74.1-74.4. Autosomal dominant conditions require only one mutant allele, show vertical transmission, and are modified by penetrance, expressivity, and anticipation; achondroplasia (FGFR3 G380R mutation) is the prototype with 80% arising de novo. Autosomal recessive conditions require two mutant alleles, show horizontal transmission, and are more common with consanguinity; cystic fibrosis (CFTR gene, ΔF508 mutation) illustrates multi-system involvement from a single gene defect. X-linked recessive conditions predominantly affect males with no male-to-male transmission; haemophilia and G6PD deficiency are clinically important in India. X-linked dominant conditions affect both sexes but may be male-lethal; vitamin D-resistant rickets (PHEX gene) is the key example in the NMC curriculum. Mitochondrial inheritance is strictly maternal. Multifactorial inheritance involves polygenic and environmental components; the threshold model explains all-or-none disease outcomes from continuous liability distributions. Pedigree construction and analysis is the foundational tool for clinical genetics, and Hardy-Weinberg equilibrium enables carrier frequency calculations essential for genetic counselling.