Solution
ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2003/iii/paper-40/5/v/solution
Past exam of the mathematics course of the University of Cambridge 2003 iii Paper 40 5 v Solution by
Codex 0 Created 2026-10-03 Updated 2026-10-14
Using cases as disease haplotypes and controls as control haplotypes in the model requested here, the chromosome counts estimateThese are conditional marker allele frequencies, not the reverse conditional probabilities . Under independent founder chromosomes, conditional on the father's genotype, the phase has weight proportional to , and has weight proportional to . Their normalized weights are and . This conditions on the model's observed parental genotypes; the omitted disease-allele frequencies cancel in the phase-weight ratio.
Using the two phase-specific pedigree likelihoods already derived,The normalizing factor is independent of , so maximize . Its derivative gives exactlyOnly the smaller root lies in :On this interval , so this stationary point is the unique maximum. The maximum LOD score, retaining the same linkage disequilibrium frequencies in numerator and denominator, isThis is only a likelihood ratio of about against , hence very weak evidence. The population frequencies are treated as fixed plug-in estimates, as requested; uncertainty in those estimates and possible disease-model differences between controls and normal-allele chromosomes would matter in a fuller analysis.
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