 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.