Two Types of Meiotic Crossovers Coexist in Maize

Abstract

We apply modeling approaches to investigate the distribution of late recombination nodules in maize (Zea mays). Such nodules indicate crossover positions along the synaptonemal complex. High-quality nodule data were analyzed using two different interference models: the "statistical" gamma model and the "mechanical" beam film model. For each chromosome, we exclude at a 98% significance level the hypothesis that a single pathway underlies the formation of all crossovers, pointing to the coexistence of two types of crossing-over in maize, as was previously demonstrated in other organisms. We estimate the proportion of crossovers coming from the noninterfering pathway to range from 6 to 23% depending on the chromosome, with a cell average of ;15%. The mean number of noninterfering crossovers per chromosome is significantly correlated with the length of the synaptonemal complex. We also quantify the intensity of interference. Finally, we develop inference tools that allow one to tackle, without much loss of power, complex crossover interference models such as the beam film. The lack of a likelihood function in such models had prevented their use for parameter estimation. This advance will allow more realistic mechanisms of crossover formation to be modeled in the future.

Meiotic Crossing Over in Maize Knob Heterochromatin

“…Crossovers visualized by MLH1 foci represent type I crossovers, i.e., those that show interference (Mercier et al 2015). In maize, mathematical modeling indicated that about 80% of the crossovers as assessed by RNs are type I crossovers with the remaining RNs (not labeled by MLH1) being type II crossovers, i.e., those that do not show interference (Falque et al 2009;Mercier et al 2015). Based on these results and an average of about 20 RNs per nucleus (Anderson et al 2003), one would expect an average of about (0.8 3 20) 16 MLH1 foci per nucleus in maize.…”

Immunocytological Analysis of Meiotic Recombination in the Gray Goose (<b><i>Anser anser</i></b>)

“…The ν values vary between 0 (no interference) to 20 (absolute interference, or only 1 crossover per chromosome) [Falque et al, 2009;Gauthier et al, 2011]. The distances were fitted to gamma distributions by a maximum-likelihood method.…”

The Chromosomes of Birds during Meiosis

“…Current evidence in yeast and other organisms indicates that MLH1 foci tag the CO events showing chiasmatic interference, while a second type of COs (non-interfering) follows a molecular pathway lacking MLH1 [reviewed in Mezard et al, 2015]. As shown in a number of plants and animals, the proportion of non-interfering COs varies from species to species, accounting for 5-30% of all CO events [de Boer et al, 2006;Falque et al, 2009]. The presence of 2 classes of COs in birds has not yet been tested, but both RNs and MLH1 foci show CO interference in birds [Pigozzi and Solari, 1997;Pigozzi, 2001].…”