Why Are X Autosome Rearrangements so Frequent in Beetles? A Study of 50 Cases

Area of Science:

• * Cytogenetics and Evolutionary Biology
• * Insect Genetics and Genomics

Background:

• * Karyotype analysis reveals chromosomal rearrangements in 10.8% of 460 studied Polyphagan Coleoptera species.
• * X-autosome rearrangements, primarily fusions, show varying frequencies related to diploid chromosome number.

Purpose of the Study:

• * To investigate the prevalence and types of X-autosome rearrangements in Polyphagan Coleoptera.
• * To understand the evolutionary implications of these rearrangements, including the role of the Y chromosome.

Main Methods:

• * Mitotic metaphase and meiotic pachytene stage analysis of karyotypes.
• * C-banding to identify heterochromatin at rearrangement junctions.

Main Results:

• * X-autosome fusions are significantly more frequent than expected, over seven times higher than autosome involvement.
• * The Y chromosome was absent in all studied karyotypes with X-autosome rearrangements, suggesting its dispensability.
• * Heterochromatin at the X-autosome junction may insulate gene expression between the gonosome and autosome.

Conclusions:

• * The high frequency of X-autosome rearrangements is attributed to the X chromosome's acrocentric morphology and the Y chromosome's dispensability.
• * These rearrangements, particularly fusions, contribute to karyotype evolution in Coleoptera.
• * The absence of the Y chromosome simplifies male meiosis by facilitating the segregation of X-autosome complexes.