Planar quadrilateral linkage, RRRR or 4R linkages have four rotating joints. There are multiple methods that make different adjustments for allele frequency and linkage disequilibrium. The exhaust valve linkage required frequent adjustment. A suggested alternative to linkage studies was the genetic association study. Historically, the throttle pedal or lever acts via a direct mechanical linkage. The transmission uses a cable shifter, unlike previous designs that use a direct mechanical linkage. Six genetic loci found by linkage are known and listed below. Evidence of a linkage at chromosome 3q26.3 is mixed. Each window has a knob with a direct mechanical linkage to the outside shutter assembly. Branched ubiquitin chains containing multiple linkage types can be formed. Polyadenylation is the covalent linkage of a polyadenylyl moiety to a messenger RNA molecule. They tend to handle more like regular bikes than cargo bikes with linkage steering. It was used by Punnett in early studies of genetic linkage. The rear suspension linkage and rear spring rate were replaced, improving handling. This proximity is used as input of average linkage hierarchical clustering.