= Solution
<Genetic linkage> analysis follows co-segregation of <genetic marker> and disease <alleles> within <pedigrees>. It estimates or tests a <recombination fraction>, with <independent assortment> at $\theta=1/2$ as the ordinary null. It can locate a disease <genetic locus> even when different families have different <genetic marker> <alleles> on their disease chromosomes.
<Genetic association> analysis tests whether <allele> or <genotype> frequencies differ with disease status. It can compare unrelated cases and controls, or compare transmitted and untransmitted parental <alleles>. A noncausal <genetic marker> can be associated through population <linkage disequilibrium> with a causal <genetic locus>. Association therefore concerns population-frequency relationships, whereas linkage concerns inheritance; <population stratification> can confound the former without producing genuine within-family linkage.
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