A karyotype of the Arabidopsis thaliana genome derived from synaptonemal complex analysis at prophase I of meiosis

Abstract

SummarySynaptonemal complex (SC) complements prepared for electron microscopy allow high-resolution chromosome analysis. SC preparations were used to determine the relative lengths of the chromosomes of the Arabidopsis thaliana genome. This complements the extensive genetic and molecular analyses of these chromosomes. The two smallest SCs (chromosomes) carry a nucleolus-organizing region (NOR) at or near one end, and at prophase I of meiosis both have a relative SC length of about 16-17% of the total complement. The three longest SCs have relative lengths of 19,22.5 and 25% and can be identified on this criterion. Fluorescent in situ hybridization with nonradioactively labelled ribosomal DNA confirmed that there are two pairs of NOR chromosomes and also showed that the ribosomal genes are localized with the nucleolus. SC formation at NORs is often interrupted and this may reduce recombination in these regions of the genome.

Sex-specific crossover distributions and variations in interference level along Arabidopsis thaliana chromosome 4

“…We found that SC length in male meiocytes is 166 6 24 lm (n ¼ 22) compared to only 98 6 20 lm (n ¼ 25) in female. Our estimate of male SC length is in good agreement with that obtained in a previous study (147 6 28 lm; n ¼ 19) using electron microscopy [40]. The value we obtained for the M/F ratio of total SC lengths is very close to that for the M/F ratio of mean CO numbers per chromosome (1.70 versus 1.76).…”

Description of 31 YAC contigs spanning the majority of Arabidopsis thaliana chromosome 5

“…These data suggest that chromosome 5 is larger than chromosome 4. This is consistent with data from Albini (1994), who has established that the two chromosomes carrying nucleolar-organizing regions, chromosomes 2 and 4, are considerably smaller than chromosomes 1, 3 and 5.…”

Detailed description of four YAC contigs representing 17 Mb of chromosome 4 of Arabidopsis thaliana ecotype Columbia

“…Thus the total size of chromosome 4 is greater than 21.5 Mb. Measurements of the synaptonemal complex length of chromosome 4 have shown that this chromosome comprises 16.8% of the genome (Albini, 1994). In the nucleolar organizing region the synaptonemal complex is interrupted and it is not clear how much of this region contributes to the entire length of the chromosome established by this method.…”