Researcher ORCID Identifier

Graduation Year


Date of Submission


Document Type

Campus Only Senior Thesis

Degree Name

Bachelor of Arts



Reader 1

Patrick Ferree

Reader 2

Brian Duistermars

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© 2023 Elizabeth J Novogradac


B chromosomes are non-essential chromosomes that are abundant in plant and animal species. Because B chromosomes are non-essential, there is no functional selection so they can be prone to loss during mitosis and meiosis. However, many B chromosomes have strange properties to transmit themselves at extraordinarily high levels; these properties are collectively referred to as chromosome drive. An extreme example of B chromosome drive is genome elimination caused by the paternal sex ratio (PSR) chromosome in the jewel wasp, Nasonia vitripennis. PSR causes complete elimination of the sperm’s genetic material during the first embryonic mitosis. Due to the haplodiploid reproduction of the wasp, this event causes female- destined diploid embryos to become haploid males. PSR itself does not undergo elimination, despite its presence with the paternal chromatin until the genome elimination event. The mechanisms by which PSR destroys the paternal genome and avoids self-destruction are not understood. To gain insights, we have introduced PSR into a sibling species, N. longicornis by interspecies genetic crosses. The goal is to examine PSR’s segregation behavior and ability to cause genome elimination when it is in a different genetic background. So far, we have successfully introduced PSR into the sibling species and found that it successfully eliminated the paternal genome, but this effect is not fully penetrant in this background. We also observed cases of incomplete segregation of PSR to the daughter nuclei of the embryo during cleavage divisions. These findings argue that there are species-level differences between the Nasonia species that affect the behavior of PSR’s genome elimination activity, despite their close evolutionary relatedness.

This thesis is restricted to the Claremont Colleges current faculty, students, and staff.