Contact zone between chromosomal races of Mus musculus domesticus. 2. Fertility and segregation in laboratory-reared and wild mice heterozygous for multiple robertsonian rearrangements.
Litter size, anaphase I nondisjunction and X-Y dissociation at metaphase I were studied in homozygous and heterozygous house mice from a central Italian chromosomal hybrid zone between the CD (2n=22) race and the standard race (2n=40). We also observed the segregation of the two chromosomal forms (Robertsonian and non-Robertsonian) in male and female multiple heterozygotes from the karyotype of their offspring and chromosomal arm counts of metaphase II. Litter size was significantly reduced in the F1 hybrids, but there was no difference in litter size between male and female F1s. Fertility in wild mice decreased with increasing numbers of structural heterozygosities (0-5). Some metacentrics appear to be under meiotic drive but there was no rule as to which of the two forms was favoured in backcrosses. An original observation of a negative correlation between the length of metacentrics and transmission rate was described in hybrids. Slight cosegregation of chromosomes with a similar morphology was present in the progeny of males and females. These observations are discussed in relation to the stability of this hybrid zone through time.
Castiglia
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R
Dipartimento di Biologia Animale e dell' Uomo, Università di Roma 'La Sapienza'-Via A. Borelli 50, 00161 Rome, Italy. Castiglia@uniroma1.it
Capanna
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E
D000705:Anaphase; D000818:Animals; D000830:Animals, Laboratory; D000835:Animals, Wild; D020090:Chromosome Segregation; D005260:Female; D005298:Fertility; D006579:Heterozygote; D006824:Hybridization, Genetic; D008098:Litter Size / Q000235:genetics; D008297:Male; D008677:Metaphase; D051379:Mice / Q000235:genetics / Q000502:physiology*; D009630:Nondisjunction, Genetic; D013045:Species Specificity; D014178:Translocation, Genetic; D014960:X Chromosome; D014998:Y Chromosome