Muller elements

(work in progress...)

Synteny conservation is even visible between fruit flies and cockroaches (Meisel, Delclos and Wexler, 2019).

Hi-C shows contacts between telomeres and between centromeres in mosquito species, and few contacts between both arms of the same chromosome (Dudchenko and coll., 2017; Copmton and coll., 2020). Note that the chromosomes of Aedes aegypti are significantly larger than what is usually found in Drosophila.

In Hoencamp and coll., 2021, centromeric clustering in Hi-C contact maps is also shown; it is hypothtised that it is because of the lack of a fully functional condensin II complex.

D. bifasciata (and other Drosophila) have large and highly repetitive pericentric regions Bracewell and coll., 2020.

RSS Atom

Ranz JM, Casals F, Ruiz A.

Genome Res. 2001 Feb;11(2):230-9. doi:10.1101/gr.162901

How malleable is the eukaryotic genome? Extreme rate of chromosomal rearrangement in the genus Drosophila.

186 DNA probes on Muller element E (density: 1 / 175 kbp in D. mel and 1 / 219 in D. rep) for comparing gene order in D. repleta and D. melanogaster. Random distribution of breakpoints. “177.07 (±28.88) breakpoints or 89 (±14) paracentric inversions fixed in this chromosomal element between D. melanogaster and D. repleta.” “Application of [a] ML method [...] yielded an estimate of 228 (±28) fixed breakpoints, that is, 114 ± 14 fixed inversions.” “We estimate an evolution rate of 0.9–1.4 chromosomal inversions fixed per million years.” “A significant correlation of gene order was found.” “If large inversions have a low probability of fixation because of their fertility effects (Navarro et al. 1997), which seems to be the case (Cáceres et al. 1997), then the randomization of gene order would proceed at a slower rate than is implied in Figure 2.”

Bracewell R, Tran A, Chatla K, Bachtrog D.

G3 (Bethesda). 2020 Mar 5;10(3):891-897. doi:10.1534/g3.119.400922

Chromosome-Level Assembly of Drosophila bifasciata Reveals Important Karyotypic Transition of the X Chromosome.

Chromosome arms do not interact much with each other. Large and highly repetitive pericentric regions in which it is hard to map the Hi-C reads.

Dudchenko O, Batra SS, Omer AD, Nyquist SK, Hoeger M, Durand NC, Shamim MS, Machol I, Lander ES, Aiden AP, Aiden EL.

Science. 2017 Apr 7;356(6333):92-95. doi:10.1126/science.aal3327

De novo assembly of the Aedes aegypti genome using Hi-C yields chromosome-length scaffolds.

Hi-C contacts between telomeres and between centromeres. Few contacts between arms of the same chromosome.

Meisel RP, Delclos PJ, Wexler JR.

BMC Biol. 2019 Dec 5;17(1):100. doi:10.1186/s12915-019-0721-x

The X chromosome of the German cockroach, Blattella germanica, is homologous to a fly X chromosome despite 400 million years divergence.

“We provide two lines of evidence that the X chromosome of the German cockroach, B. germanica, is homologous to Muller element F, which is X-linked in most flies. First, there is a reduced sequencing coverage of nearly half of the Muller element F homologs in male cockroach, consistent with a haploid dose of the X chromosome in males (Fig. 2). Second, there is a decreased heterozygosity of element F homologs in male cockroach, including those with reduced male sequencing coverage (Fig. 3). We therefore hypothesize that element F is an ancient X chromosome that was present in the most recent common ancestor (MRCA) of flies and cockroaches, and it has been conserved as an X chromosome in the German cockroach and many fly species.”