Alternatively, a pericentromeric exchange may protect the bivalent from maternal-age related risk factors. A transition refers to an observed change in marker state from non-reduced N to reduced Ror vice versa, in two non-disjoined strands. We discuss alternative evolutionary models, which fall broadly into two categories: either the chain is the result of a sequence of translocation events from an ancestral pair of sex chromosomes Model I or the entire chain came into being at once by hybridization of two populations with different chromosomal nondisjunction of sex chromosome in Canberra sharing monobrachial homology Model II.
CRC, Boca Raton, pp37— This same risk factor has been established in model organisms as well  — . The proportions of the meiotic and mitotic errors types were taken from data collected through the Atlanta Down Syndrome Project  and unpublished results. Advanced maternal age and the risk of Down syndrome characterized by the meiotic stage of chromosomal error: a population-based study.
Hum Mol Genet 3: —
In the remaining 10 cases we observed a change in marker state see Materials and Methodsfrom N to R or vice versa, between the proximal loci on one chromosome arm and the proximal loci on the other chromosome arm. Interestingly, BubR1, the protein required for the localization of shugoshin to the centromere, has been shown to have decreased expression with increasing maternal age in the human female .
However, our sample sizes limited our ability to do so see Table S1. Parental origin of the extra chromosome in trisomy 21 as indicated by analysis of DNA polymorphisms. For example, in maternal MI errors, there is a direct correlation between exchange frequency and maternal age for trisomy 15 9but no such effect has been reported for other autosomal trisomies; in maternal MII errors, increases in maternal nondisjunction of sex chromosome in Canberra are associated with both trisomies 18 and 21, but recombination is normal for trisomy 18 and increased for trisomy For chromosome 21 MI errors, we do not see this pattern.
An example of the former would be that a pericentromeric exchange compromises proteins involved in centromeric cohesion, exacerbating the normal degradation of this important complex with age. Estimating meiotic exchange patterns from recombination data: an application to humans.
Replacing smoking with vaping during pregnancy: impacts on metabolic health in mice. Santos O, Luykx P Holozygosity for sex-linked genes in males of the termite Incisitermes schwarzi.