Nondisjunction frequencies in Robertsonian heterozygotes from natural populations of the common shrew, <i>Sorex araneus</i> L.

Abstract

Pregnant female common shrews were collected from an area of Robertsonian polymorphism, involving five different arm combinations, around Oxford (England). The females and their fetuses were karyotyped, and the karyotypes of the sires were deduced. Ten pregnancies where at least one parent was known to be either a single or double Robertsonian heterozygote were available for analysis. From these pregnancies, upper and lower estimates of anaphase I nondisjunction arising from Robertsonian heterozygosity were calculated to be 1.0–2.5% per heterozygous arm combination and 1.5–3.7% per heterozygous parent. One trisomic fetus with retarded development was identified. This trisomy can be attributed to anaphase I nondisjunction of a trivalent in a female Robertsonian heterozygote.

Preferential segregation of metacentric chromosomes in simple Robertsonian heterozygotes of Sorex araneus

“…Studies of meiosis in S. araneus have so far focused on the conjugation or the lack of pairing and non-disjunction of chromosomes in the context of impairment of fertility in heterozygotes (see Searle, 1986b;Banaszek et al, 2002). Wyttenbach et al (1998) considered the mechanisms of unequal transmission of metacentrics and concluded that any verification of their hypotheses would require a detailed analysis of the products of meiosis in heterozygotes.…”

“…Wyttenbach et al (1998) considered the mechanisms of unequal transmission of metacentrics and concluded that any verification of their hypotheses would require a detailed analysis of the products of meiosis in heterozygotes. To date, however, only segre-gation of the sex chromosomes in S. araneus has been studied in detail, initially on very limited material (Fedyk, 1980;Searle, 1986b), and more recently (following modification of the meiotic preparation technique) on large numbers of metaphase II (MII) cells (Fedyk et al, 2005). In the present paper, we report the results of analysis of products of chromosome segregation at meiosis among simple Robertsonian (Rb) heterozygous male subjects.…”

The complex Robertsonian system of Dichroplus pratensis (Melanoplinae, Acrididae). I. Geographic distribution of fusion polymorphisms

“…However, aneuploidy and macrospermatid production increase with the number of heterozygous fusions (Bidau and Mirol, 1988) which could explain the higher frequencies of fusion metacentrics in populations with 3 fusions in order to minimise the frequencies of double and triple heterozygotes (Tosto, 1989;Tosto and Bidau, 1991). In comparable stable multiple polymorphisms such as those of the common shrew, heterozygotes do not have their fertility severely reduced (Searle, 1984(Searle, , 1988Garagna et al, 1989;Searle et al, 1990).…”

The litter size in chromosomally polymorphic blue foxes

“…In the meiosis of heterozygous carriers, the translocation chromosome and its acrocentric homologues form a heterotrivalent and segregation proceeds in a fairly regular way to produce chromosomaliy balanced gametes. Nevertheless, it is presumed that, up to a certain degree, the heterotrivalent segregates non-disjunctionally at the first meiotic division (SEARLE 1986). This could result in chromosomally unbalanced gametes, which would cause embryonic aneuploidy and early embryonic death and, thus, a reduction of fertility.…”