B chromosomes are found in numerous plants and animals. These nonessential, supernumerary chromosomes are often composed primarily of noncoding DNA repeats similar to those found within transcriptionally "silenced" heterochromatin. In order to persist within their resident genomes, many B chromosomes exhibit exceptional cellular behaviors, including asymmetric segregation into gametes and induction of genome elimination during early development. An important goal in understanding these behaviors is to identify unique B chromosome sequences and characterize their transcriptional contributions. We investigated these properties by examining a paternally transmitted B chromosome known as paternal sex ratio (PSR), which is present in natural populations of the jewel wasp Nasonia vitripennis. To facilitate its own transmission, PSR severely biases the sex ratio by disrupting early chromatin remodeling processes. Through cytological mapping and other approaches, we identified multiple DNA repeats unique to PSR, as well as those found on the A chromosomes, suggesting that PSR arose through a merger of sequences from both within and outside the N. vitripennis genome. The majority of PSR-specific repeats are interspersed among each other across PSR's long arm, in contrast with the distinct "blocks" observed in other organisms' heterochromatin. Through transcriptional profiling, we identified a subset of repeat-associated, small RNAs expressed by PSR, most of which map to a single PSR-specific repeat. These RNAs are expressed at much higher levels than those arising from A chromosome-linked repeats, suggesting that in addition to its sequence organization, PSR's transcriptional properties differ substantially from the pericentromeric regions of the normal chromosomes.

We present a genome assembly from an individual Limnephilus lunatus (a caddisfly; Arthropoda; Insecta; Trichoptera; Limnephilidae). The genome sequence is 1,270 megabases in span. Most of the assembly is scaffolded into 13 chromosomal pseudomolecules, including the assembled Z chromosome. The mitochondrial genome has also been assembled and is 15.4 kilobases long.

We present a genome assembly from an individual Limnephilus marmoratus (a caddisfly; Arthropoda; Insecta; Trichoptera; Limnephilidae). The genome sequence is 1,630 megabases in span. Most of the assembly (99.93%) is scaffolded into 30 chromosomal pseudomolecules, including the assembled Z sex chromosome. The mitochondrial genome has also been assembled and is 15.4 kilobases in length.

We present a genome assembly from an individual male Leuctra nigra (black needle fly; Arthropoda; Insecta; Plecoptera; Leuctridae). The genome sequence is 536.3 megabases in span. Most of the assembly is scaffolded into 13 chromosomal pseudomolecules, including the X sex chromosome. The mitochondrial genome has also been assembled and is 17.6 kilobases in length.

We present a genome assembly from an individual male Nemurella pictetii (Arthropoda; Insecta; Plecoptera; Nemouridae). The genome sequence is 257 megabases in span. The majority of the assembly (99.79%) is scaffolded into 12 chromosomal pseudomolecules, with the X sex chromosome assembled. The X chromosome was found at half coverage, but no Y chromosome was found. The mitochondrial genome was assembled, and is 16.0 kb in length.