Because autosomal pair No. 6 is the only pair in the A karyotype that reveals co-located histone, AMG-208 structure18S rDNA, MS3 and MS7 internet sites , we advise that this pair might be the B chromosome ancestor. Remarkably, the least spanning trees attained from MS3 and MS7 satDNA sequences also supported the hypothesis of an intraspecific origin due to the substantial similarity, and even shared haplotypes, involving the sequences positioned on the A and B chromosomes of M. sanctaefilomenae. Nevertheless, the actuality that 52% of the MS3 and 100% of the MS7 sequences noticed on B2 corresponded to the most regular haplotype observed in the Illumina reads from the B-missing and B-carrying populations, while these figures were and six%, respectively, for B1, implies that the two B chromosomes arose independently from autosome six, such that in the most recent B sort , quite a few satDNA repeats of the commonest haplotype in the A genome, discovered even in distant populations, are conserved. The observed differences in satellite DNA sequences in between the two B variants also advise that concerted evolution could act individually for each B kind. Remarkably, MS3 and MS7 nucleotide range is decrease in B1, maybe simply because of its better chance of sequence homogenization because of to its better age and populace frequency. In the grasshopper Eyprepocnemis plorans, males with two or additional B chromosomes form chiasmated B-bivalents during meiosis, which helps to clarify the noticed variation in the volume of distally found 45S ribosomal DNA. Also, in M. sanctaefilomenae, the recurrent existence of cells with two or more B1 chromosomes would allow the formation of B-bivalents during meiosis and achievable unequal crossovers, yielding sequence homogenization. The actuality that B1 demonstratesPHT-427 nearly twice the dS value for H3.2 histone genes as B2 also supports the summary that B1 is older than B2.As soon as they originate, B chromosomes are subjected to almost the similar genetic circumstances that influence the molecular evolution of sexual intercourse chromosomes, especially concerning the degeneration of the heteromorphic Y or W chromosomes, which involves loss of the two functional loci and sequence homology with the standard genome as very well as heterochromatin gains. In this context, if B2 was derived from B1, it would be surprising for the young B chromosome to be heterochromatic. However, their divergent C-banding responses might not be connected with their relative ages, but with their independent origins and distinctions in 18S rDNA contents.