# A male-transmitted B chromosome undergoes strong meiotic drag in females of the jewel wasp Nasonia vitripennis

## TL;DR

This study explores how a selfish B chromosome in jewel wasps spreads through strong paternal transmission and is limited by female meiotic drag and copy number restriction.

## Contribution

The study reveals hidden female meiotic drag and copy number restriction as key mechanisms for the inheritance of a selfish B chromosome in jewel wasps.

## Key findings

- PSR is transmitted paternally but shows reduced transmission in females due to meiotic drag.
- PSR is restricted to a single copy per genome, as two copies are lethal to wasp development.

## Abstract

Many organisms carry extra, non-essential chromosomes known as B chromosomes (Bs), which are selfishly transmitted at super-mendelian levels to offspring. This heightened transmission, termed drive, occurs during gametogenesis, usually in one of the two parents. In some cases, Bs can experience an opposing process, drag, which reduces their transmission. If these processes occur together in the same organism, one in each parental sex, then they may facilitate the spread of Bs while countering their accumulation in the genome to harmful levels. While previous studies have elucidated mechanistic aspects of B drive, little is known about drag or other factors that govern the inheritance of these selfish genetic elements. Here, we examined the inheritance of Paternal Sex Ratio (PSR), a single-copy B in the jewel wasp, Nasonia vitripennis, which is transmitted paternally to offspring. PSR drives by converting female-destined embryos into PSR-transmitting males. Using genetic manipulation, we produced exceptional PSR-carrying females, which were used to assess B transmission potential. We found that females transmit PSR at an unexpectedly low level compared to univalent chromosomes in other organisms. This reduced transmission stems from remarkable loss of PSR from the egg’s nucleus upon entry into meiosis, an effect that may be caused by an absence of microtubule-based spindle fibers in meiosis I-arrested wasp eggs. We also found that PSR is strictly limited to a single copy per genome, likely because wasps having two PSR copies die during development. Our findings reveal the successful inheritance of this selfish B chromosome involves its restriction to a single copy and hidden female meiotic drag in addition to strong paternal drive.

Many organisms carry non-essential, selfish B chromosomes that spread through super-Mendelian transmission, but opposing forces like drag can limit their accumulation. This study shows that the Paternal Sex Ratio (PSR) chromosome in the jewel wasp achieves successful inheritance through strong paternal drive, hidden female meiotic drag, and restriction to a single copy.