Joined the Department in 2018
- 2015 Ph.D., Quantitative Biology, University of Texas at Arlington
- 2010 B.S., Environmental Science, Oregon State University, Summa Cum Laude
Genetics Society of America; Society for the Study of Evolution, American Genetics Association;
Coleopterists Society; American Society of Naturalists
The Blackmon Lab is in the Biology Department at Texas A&M University. We have two broad areas of inquiry. The first is genome evolution, specifically sex chromosome and structural evolution. The second is the development of methods and databases that accelerate the analysis of data within a quantitative genetic or phylogenetic framework. To address these topics, we use a broad range of approaches including theoretical population genetics, bioinformatics, genomics, and molecular cytogenetics. Although we have projects involving all types of organisms, we often study beetles, and we keep several species in the lab as model organisms.
Fragile Y Hypothesis
Chromosomal sex determination is phylogenetically widespread, having arisen independently in many lineages. Decades of theoretical work provide predictions about sex chromosome differentiation that are well supported by observations in both XY and ZW systems. However, the phylogenetic scope of previous work gives us a limited understanding of the pace of sex chromosome gain and loss and why Y or W chromosomes are more often lost in some lineages than others, creating XO or ZO systems. Contrary to our initial expectations, we find that highly degenerated Y chromosomes of many members of the Coleoptera suborder Polyphaga are rarely lost and that cases of Y chromosome loss are strongly associated with chiasmatic segregation during male meiosis. We propose the “Fragile Y Hypothesis” that recurrent selection to reduce recombination between the X and Y chromosome leads to the evolution of a small pseudoautosomal region, which, in taxa that require XY chiasmata for proper segregation during meiosis, increases the probability of aneuploid gamete production, with Y chromosome loss. This hypothesis predicts that taxa that evolve achiasmatic segregation during male meiosis will rarely lose the Y chromosome.
The pace and direction of evolution are governed by the genetic architecture of trait variation. Evolutionary biologists have disagreed about whether genes can be considered to act in isolation, or in the context of their genetic background (Fisher Wright debate). Line cross analysis (LCA) estimates genetic architecture parameters conditional on the best model chosen from a vast model space using relatively few line means and ignores uncertainty in model choice. To address these issues, we introduced an information theoretic approach to LCA, which comprehensively assesses the potential model space, quantifies model selection uncertainty, and uses model weighted averaging to estimate composite genetic effects accurately. Using simulated data and previously published LCA studies we have shown the utility of our approach to define the components of complex genetic architectures. Our analysis of 20+ previously published datasets also shows that traditional approaches have underestimated the importance of epistasis.
Insects exhibit variation in both chromosome number and sex chromosome systems. Insect karyotypes have been an important source of data for both taxonomic and basic evolutionary biology research. Unfortunately, this data has always been scattered among journals and dissertations that are not accessible without subscriptions. We created the Tree of Sex Database to make this data open and available to all researchers. We curate the insect portion of this database that currently has over 15,000 records and has proven to be a valuable resource to explore and test ideas about the evolution of high-level genome evolution. Recently we published a synthesis of this vast dataset and uncovered many interesting patterns and avenues for future investigations. We also recently published a subset of this data as the Coleoptera Karyotype Database. Beetle karyotypes are particularly powerful since they normally include information about the meiotic behavior of sex chromosomes.
It has long been thought that in Eusocial insect selection to increase genetic diversity within a colony should indirectly select for increases in the number of chromosomes. To test this long-standing hypothesis, we investigated the relationship between eusociality and chromosome number across Hymenoptera. We found that solitary and social Hymenoptera do not have significantly different numbers of chromosomes. However, we did find that chromosome number evolves more quickly in social than solitary Hymenoptera. It remains unclear whether variable selection pressure or drift are responsible for this difference.
- Hjelmen, CE, Holmes, VR, Burrus, CG, Piron, E, Mynes, M, Garrett, MA et al.. Thoracic underreplication in Drosophila species estimates a minimum genome size and the dynamics of added DNA. Evolution. 2020; :. doi: 10.1111/evo.14022. PubMed PMID:32438451 .
- Lo, J, Jonika, MM, Blackmon, H. micRocounter: Microsatellite Characterization in Genome Assemblies. G3 (Bethesda). 2019;9 (10):3101-3104. doi: 10.1534/g3.119.400335. PubMed PMID:31375475 PubMed Central PMC6778809.
- Hjelmen, CE, Blackmon, H, Holmes, VR, Burrus, CG, Johnston, JS. Genome Size Evolution Differs Between Drosophila Subgenera with Striking Differences in Male and Female Genome Size in Sophophora. G3 (Bethesda). 2019;9 (10):3167-3179. doi: 10.1534/g3.119.400560. PubMed PMID:31358560 PubMed Central PMC6778784.
- Perkins, RD, Gamboa, JR, Jonika, MM, Lo, J, Shum, A, Adams, RH et al.. A database of amphibian karyotypes. Chromosome Res. 2019;27 (4):313-319. doi: 10.1007/s10577-019-09613-1. PubMed PMID:31338646 .
- Schield, DR, Card, DC, Hales, NR, Perry, BW, Pasquesi, GM, Blackmon, H et al.. The origins and evolution of chromosomes, dosage compensation, and mechanisms underlying venom regulation in snakes. Genome Res. 2019;29 (4):590-601. doi: 10.1101/gr.240952.118. PubMed PMID:30898880 PubMed Central PMC6442385.
- Armstrong, A, Anderson, NW, Blackmon, H. Inferring the potentially complex genetic architectures of adaptation, sexual dimorphism and genotype by environment interactions by partitioning of mean phenotypes. J. Evol. Biol. 2019;32 (4):369-379. doi: 10.1111/jeb.13421. PubMed PMID:30698300 .
- Blackmon, H, Justison, J, Mayrose, I, Goldberg, EE. Meiotic drive shapes rates of karyotype evolution in mammals. Evolution. 2019;73 (3):511-523. doi: 10.1111/evo.13682. PubMed PMID:30690715 PubMed Central PMC6590138.
- Passow, CN, Bronikowski, AM, Blackmon, H, Parsai, S, Schwartz, TS, McGaugh, SE et al.. Contrasting Patterns of Rapid Molecular Evolution within the p53 Network across Mammal and Sauropsid Lineages. Genome Biol Evol. 2019;11 (3):629-643. doi: 10.1093/gbe/evy273. PubMed PMID:30668691 PubMed Central PMC6406535.
- Blackmon, H, Brandvain, Y. Long-Term Fragility of Y Chromosomes Is Dominated by Short-Term Resolution of Sexual Antagonism. Genetics. 2017;207 (4):1621-1629. doi: 10.1534/genetics.117.300382. PubMed PMID:29021279 PubMed Central PMC5714469.
- Adams, RH, Schield, DR, Card, DC, Blackmon, H, Castoe, TA. GppFst: genomic posterior predictive simulations of FST and dXY for identifying outlier loci from population genomic data. Bioinformatics. 2017;33 (9):1414-1415. doi: 10.1093/bioinformatics/btw795. PubMed PMID:28453670 .