The effects of Robertsonian fusions on chiasma frequency and distribution in the house mouse (Mus musculus domesticus) from a hybrid zone in northern Scotland

Abstract

Chiasma frequency and distribution were studied in male Mus musculus domesticus from the John O'Groats±standard chromosomal hybrid zone in northern Scotland. Individuals of the John O'Groats race (2n 32; homozygous for the Robertsonian fusions 4.10, 6.13, 9.12 and 11.14) and the standard race (2n 40, all telocentric), and hybrids with various karyotypes, were examined. Chiasma frequency was signi®cantly negatively correlated with the number of Robertsonian con®gurations in the meiotic cell. The decrease of chiasma frequency can be attributed to intrachromosomal eects that reduce the number of chiasmata in Robertsonian bivalents (formed in homozygotes for Robertsonian fusions) and trivalents (formed in heterozygotes). However, the reduction is more pronounced in Robertsonian bivalents and is related to a shift of chiasmata to the distal ends of the chromosome arms. A dierent type of repatterning occurs in trivalents where there is a signi®cant increase in proximal and interstitial chiasmata.

Reduced recombination patterns in Robertsonian hybrids between chromosomal races of the house mouse: chiasma analyses

“…In house mice, the intensity of the decrease in recombination rates in Rb fusions varied slightly among geographic regions and chromosomal races, irrespective of the method of analysis (chiasma or MLH1; range: 22.16oSto23.0; 20.1oRbo22.28; the present study; Wallace et al, 1992;Bidau et al, 2001;Castiglia and Capanna, 2002;Dumas and Britton-Davidian, 2002;Merico et al, 2013). Exceptionally high levels were observed by Merico et al (2003) in two North Italian races (Rb ¼ 24.58; St ¼ 25.13) that exceeded estimates described so far for the subspecies (Dumont and Payseur, 2011).…”

“…To our knowledge, few analyses on chiasma or MLH1 patterns have compared trivalent-carrying heterozygous wild mice with homozygous standard or Rb individuals, and those that have, involve either few cells (that is, 12 cells; Wallace et al, 1992), few Rb fusions (that is, 4; Bidau et al, 2001) or mostly polymorphic hybrid karyotypes (24o2no39; Castiglia and Capanna, 2002;Capilla et al, 2014). The exception is the study by Merico et al (2003) involving other North Italian races (2n ¼ 24, St mice) and their laboratory-bred F1 hybrids (2n ¼ 32 with eight trivalents).…”

“…Analyses of recombination rates in wild Rb heterozygotes have also been assessed but involve, in most cases, polymorphic individuals, that is, carrying variable numbers of Rb bivalents and trivalents, making it difficult to disentangle the effect of each meiotic type of configuration (Wallace et al, 1992;Bidau et al, 2001;Castiglia and Capanna, 2002;Capilla et al, 2014). In contrast, extensive analyses of recombination patterns in single-Rb heterozygotes have been performed by genetic assays in crosses between different laboratory strains (Davisson and Akeson, 1993).…”

Origin of the chromosomal radiation of Madeiran house mice: a microsatellite analysis of metacentric chromosomes

“…It has been demonstrated that house mice heterozygous for metacentrics have impaired reproductive fitness (for example, Wallace et al, 1992Wallace et al, , 2002Saïd et al, 1993;Hauffe and Searle, 1998), and that there are recombination effects in the vicinity of the centromere in such heterozygotes (for example, Davisson and Akeson, 1993;Bidau et al, 2001;Merico et al, 2003). Thus, one or both of these processes could affect gene flow in the centromeric region of the metacentric chromosomes investigated by us.…”

Contact zones between chromosomal races of Mus musculus domesticus. 3. Molecular and chromosomal evidence of restricted gene flow between the CD race (2n = 22) and the ACR race (2n = 24)

“…Since structural heterozygosity is expected to reduce the fitness of hybrid individuals, gene flow between races should be reduced. Moreover, gene flow can be affected by chiasma repatterning accompanying the chromosomal rearrangements (Bidau et al, 2001;Rieseberg, 2001;Castiglia and Capanna, 2002). A number of chromosomal hybrid zones between chromosomal races, differing in the number and identity of metacentrics, have been investigated to try to answer the question.…”