This is the blog for GW students taking Human Evolutionary Genetics. This site is for posting interesting tidbits on: the patterns and processes of human genetic variation;human origins and migration; molecular adaptations to environment, lifestyle and disease; ancient and forensic DNA analyses; and genealogical reconstructions.

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Monday, February 17, 2020

Time lapse: A glimpse into prehistoric genomics


Time lapse: A glimpse into prehistoric genomics
Darren K. Griffin, Denis M. Larkin, Rebecca E. O'Connor

This study is brief introduction to the reconstruction of ancestral karyotypes in extant species, specifically theropod dinosaur lineage using extant avian chromosome level genome assemblies.  This allows for a “complete” reconstruction to occur (chromosome level). Genomic structure is the way that genes are arranged on chromosomes and is species specific.


They used ancestral genome reconstruction tools Multiple Genome Rearrangement and Analysis MGRA, to identify nineteen contiguous ancestral regions (CARs). These were then used to compare the diapsid ancestor and chicken genomes.

They first determine the likely karyotype of the avian ancestor that would be most similar to a chicken or turkey. They then found the most likely karyotype for this ancestral bird-lizard and the chromosomal changes that took place between now and then. Several translocations and inversions (two main changes) took place from a lizard-like genome structure to that of soft-shelled turtles (275-255 mya). Due to the karyotypic similarities, there were few changes from this early ancestor to the beginning of dinosaurs and pterosaurs, to the theropod lineage and to modern birds. This shows that was an avian-like karyotype in place roughly 240 mya. After the Chicxulub meteor, there was an increased period of avian speciation with 36 lineages appearing over 10-15 million years.

The avian-like karyotype has many micro chromosomes that allows for variation through random segmentation and recombination. The authors believe that this driver of natural selection allowed for dinosaurs to survive multiple extinction events, becoming more diverse and speciose over time. This paper briefly reviews the genome organization and evolution of ancient chromosomes and their impact on phenotypic diversity, evolution, and adaptation.

Kailie Batsche
18 February 2020 Potluck



Griffin, D. K., Larkin, D. M., & O’Connor, R. E. (2019). Time lapse: A glimpse into prehistoric genomics. European Journal of Medical Genetics, 63(2), 103640. https://doi.org/10.1016/j.ejmg.2019.03.004

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