Abstract
The efficiency of natural and artificial selection is critically dependent on the recombination rate. However, interbreed and individual variation in recombination rate in poultry remains unknown. Conventional methods of analysis of recombination such as genetic linkage analysis, sperm genotyping and chiasma count at lampbrush chromosomes are expensive and time-consuming. In this study, we analyzed the number and distribution of recombination nodules in spermatocytes of the roosters of six chicken breeds using immunolocalization of key proteins involved in chromosome pairing and recombination. We revealed significant effects of breed (; ) and individual (; ) on variation in the number of recombination nodules. Both interbreed and individual variations in recombination rate were almost entirely determined by variation in recombination density on macrochromosomes, because almost all microchromosomes in each breed had one recombination nodule. Despite interbreed differences in the density of recombination nodules, the patterns of their distribution along homologous chromosomes were similar. The breeds examined in this study showed a correspondence between the age of the breed and its recombination rate. Those with high recombination rates (Pervomai, Russian White and Brahma) are relatively young breeds created by crossing several local breeds. The breeds displaying low recombination rate are ancient local breeds: Cochin (Indo-China), Brown Leghorn (Tuscany, Italy) and Russian Crested (the European part of Russia).
Highlights
Recombination makes a substantial contribution to genetic and phenotypic variability
Data obtained to date indicate much higher and less variable recombination rate in birds compared to mammals (Semenov et al, 2018)
We estimated the number and distribution of recombination events in the rooster genome by immunolocalization of MLH1 protein, a reliable marker of mature recombination nodules
Summary
Recombination makes a substantial contribution to genetic and phenotypic variability. Data obtained to date indicate much higher and less variable recombination rate in birds compared to mammals (Semenov et al, 2018). Low interspecies variation in recombination rate is usually explained by a low variation in chromosome number. In most birds, it is almost the same (2n = 78–80) (Griffin et al, 2007). Malinovskaya et al (2018) demonstrated that the bird species that differ substantially in chromosome number may have the same recombination rate. The species with the same chromosome number show significant differences in recombination rate (Calderon and Pigozzi, 2006; Semenov et al, 2018)
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