Where does crossover collide?

The exchange of matching segments between paired chromosomes during the formation of egg and sperm cells, which reshuffles the versions of genes a parent passes on. Morgan's 1911 Random segregation versus coupling in Mendelian inheritance proposed that linked traits separate more often the farther apart they lie along a chromosome, and Sturtevant's 1913 The linear arrangement of six sex-linked factors in Drosophila turned that idea into the first genetic map by using how often crossover occurs as a measure of distance. Here the word names a physical swap of genetic material inside a cell, counted as a recombination rate, and it has nothing to do with a study design that gives each patient every treatment in turn or the passing of one partner's stress to the other.[1][2]

Unit

One exchange event between homologous chromosomes, scaled as a recombination frequency between two locations on a chromosome

Recovery means

Not applicable

Measured by

Estimated from the proportion of offspring showing recombined trait combinations, expressed in map units (centimorgans)

A study design in which each participant receives the treatments being compared one after another, so that every person acts as their own comparison. Grizzle's 1965 The two-period change-over design and its use in clinical trials set out how to analyse the common form in which subjects are split into two orders, given treatment A then B or B then A, and compared within themselves while the analysis checks for effects that carry from the first period into the second. Here the word names an arrangement of who gets which treatment and when, judged by how cleanly the treatment effect can be separated from order and carryover, unlike a swap of chromosome segments or the passing of strain between two people.[3]

Unit

One study design in which subjects cross from one treatment to another in sequence

Recovery means

A washout period is left between treatments so the effect of the first does not carry into the next

Measured by

Assessed by the within-subject difference between treatments, with statistical tests for period and carryover effects

The transfer of stress or strain from one person to another who is close to them, most often between partners in a couple. Westman's 2001 Stress and strain crossover gathered scattered findings into one framework, describing how one partner's job demands and resulting strain show up as strain in the other through shared circumstances, empathy, and daily interaction. Here the word names a transmission of psychological states between two people, measured by how one person's strain predicts the other's, and it is unrelated to a swap of genetic material or a sequence of treatments given to a single patient.[4]

Unit

One instance of strain passing from one partner to the other

Recovery means

Not applicable

Measured by

Assessed by how strongly one partner's reported strain predicts the other's after accounting for their shared setting