Abstract
Benef its and costs of meiotic recombination are a matter of discussion. Because recombination breaks allele combinations already tested by natural selection and generates new ones of unpredictable f itness, a high recombination rate is generally benef icial for the populations living in a f luctuating or a rapidly changing environment and costly in a stable environment. Besides genetic benef its and costs, there are cytological effects of recombination, both positive and negative. Recombination is necessary for chromosome synapsis and segregation. However, it involves a massive generation of double-strand DNA breaks, erroneous repair of which may lead to germ cell death or various mutations and chromosome rearrangements. Thus, the benef its of recombination (generation of new allele combinations) would prevail over its costs (occurrence of deleterious mutations) as long as the population remains suff iciently heterogeneous. Using immunolocalization of MLH1, a mismatch repair protein, at the synaptonemal complexes, we examined the number and distribution of recombination nodules in spermatocytes of two chicken breeds with high (Pervomai) and low (Russian Crested) recombination rates and their F1 hybrids and backcrosses. We detected negative heterosis for recombination rate in the F1 hybrids. Backcrosses to the Pervomai breed were rather homogenous and showed an intermediate recombination rate. The differences in overall recombination rate between the breeds, hybrids and backcrosses were mainly determined by the differences in the crossing over number in the seven largest macrochromosomes. The decrease in recombination rate in F1 is probably determined by diff iculties in homology matching between the DNA sequences of genetically divergent breeds. The suppression of recombination in the hybrids may impede gene f low between parapatric populations and therefore accelerate their genetic divergence.
Highlights
Benefits and costs of meiotic recombination are a favorite subject of theoretical discussions and mathematical mo dels (Kondrashov, 1993; Otto, Lenormand, 2002; Hartfield, Keightley, 2012; Rybnikov et al, 2020)
We examine the inheritance of the recombina tion rate in male F1 hybrids and backcrosses of the chicken breeds showing the highest (Pervomai) and lowest (Russian Crested) level of recombination among the six breeds exa mined by L.P
The backcrosses were homogeneous for the number of MLH1 foci (Fig. 3). They demonstrated a low average MLH1 foci number (62.6 ± 0.5), typical for the Russian Crested ( p = 0.80), they exceeded F1 hybrids in this trait ( p < 10–6). These results indicate negative heterosis of the recombination rate measured as MLH1 foci number per pachytene cell
Summary
Benefits and costs of meiotic recombination are a favorite subject of theoretical discussions and mathematical mo dels (Kondrashov, 1993; Otto, Lenormand, 2002; Hartfield, Keightley, 2012; Rybnikov et al, 2020). They are mostly focused on the population genetic effects of recombination, i. Besides genetic benefits and costs, there are cytological effects of recombination, both positive and negative. Recombination is necessary for chromosome synapsis and segregation. It involves a massive generation of double-strand DNA breaks. Insufficient or er roneous repair of the breaks leads to the death of the affected germ cells or various mutations and chromosome rearrange ments (Zickler, Kleckner, 2015)
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