Discipline: Biological Sciences
Krislen Tison - University of the Virgin Islands
Co-Author(s): Max Bernstein and Matthew Rockman, New York University
Homologous recombination during meiosis I in eukaryotes is a fundamental process that allows for proper chromosome segregation and exchange of unique genetic material. It is a major mechanism by which diversity amongst organisms is driven. The formation of crossovers in most organisms is tightly regulated, whereby chromosomes experience few crossovers relative to the number of double-strand breaks created. However, in Caenorhabditis elegans (C. elegans) crossovers occur only once per chromosome pair. Such a low frequency points to what is called a nearly complete crossover interference meaning that interference extends across the entire length of the chromosome. This extreme occurrence has not been found in any other organism. The phenomenon of crossover interference is characterized as the development at which one crossover hinders the existence for other multiple proximal crossovers to occur. Our interest lies in examining whether the event is present in other nematodes within the Caenorhabditis genus. The objective of this study was to investigate the phenomenon of extreme crossover interference on Chromosome II for Caenorhabditis. sp. 29 (sp. 29) and Caenorhabditis briggsae (C. briggsae), with the intention of comparing the findings to that of C. elegans. Here we test the hypothesis that C. elegans, C. sp.29, and C. briggsae will demonstrate similar patterns of extreme crossover interference, despite C. sp. 29 being an outgroup. Experimentation for this study involved genetic crossings of worms from the same species and fertilization during the L4 stage, DNA extraction followed by polymerase chain reaction, and lastly identification of crossovers based on specific markers (genotyping). In total, 180 C. briggsae and 97 C. elegans strains were successfully genotyped where C. briggsae has 107 zero crossovers, 71 single crossovers and 2 double crossover while C. elegans has 47 zero crossovers 49 single crossovers, 1 double crossover. Data for sp. 29 were inconclusive as troubleshooting issues hindered the progression of data collection. A Fisher’s exact test was conducted to test differentiation between non-recombinant and recombinant chromatids based on a 50-50 recombination expectation. The statistics show that C. briggsae has a P-value of 0.0568 and C. elegans a P-value of 1.0000 meaning that there is no significant difference between the observed and the 50-50 expected recombination occurrence. These results suggest that C. briggsae worms are experiencing similar crossover interference as C. elegans. Future directions of this study involves finishing experimentation for sp.29 data as well as identifying the phenomenon of nearly complete crossover interference in other nematodes under the C. elegans super-group and the possible evolutionary aspects of the occurrence.
Funder Acknowledgement(s): National Institute of Health
Faculty Advisor: Matthew Rockman, firstname.lastname@example.org
Role: I did all parts of the research which involved genetic crossings of worms, DNA extraction, polymerase chain reaction (PCR), genotyping, and Statistics.