Genome Sequencing and Dating

Heres a question that i didnt know how to research, How do scientists know how when the last time a divergance took place? For example, its said Cat and Human dna is 90% similar and diverged 100 million years ago? How is that done?

Cheers:)

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It appears the question is in regards to DNA dating. It is based on the number of mutations D, rate of mutation R, and time of divergence (T). The approximate formula with some simplifications is: D = 2TR. If you know D and R, just solve for T.

Dr. Swamidass In the above example between Cats and humans what D and R would I use in the formula?

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Good question.

I don’t have time to track that down right this moment, but I will show you how. Also to compute it accurately, you have to go to more accurate formulas. The best resources for this is: http://www.timetree.org/.

Putting in “cat” and “human” into the divergence time, we get this graph. Each black dot is a different study’s estimate. There are estimates by several genetic methods, and some by the fossil record. The median estimate of 56 studies is 96 million years ago, which is during the age of dinosaurs.

human_domestic%20cat_divergence%20time

On the web page, there are several studies which can be looked at more closely to untangle the exact data. From some of these, you will be able to see the D and the R, and the more accurate formulas too.

Time Title Reference Year
88.0 Primate phylogenetic relationships and divergence dates inferred from complete mitochondrial genomes. Pozzi et al. 2014
101.6 The evolution of bat vestibular systems in the face of potential antagonistic selection pressures for flight and echolocation. Davies et al. 2013
94.5 The draft genomes of soft-shell turtle and green sea turtle yield insights into the development and evolution of the turtle-specific body plan. Wang et al. 2013
79.9 Evolutionary history of lagomorphs in response to global environmental change. Ge et al. 2013
88.6 Evaluating purifying selection in the mitochondrial DNA of various mammalian species. Soares et al. 2013
81.3 Did the expansion of C4 plants drive extinction and massive range contraction of micromammals? Inferences from food preference and historical biogeography of pikas Ge et al. 2012
83.0 The development of three long universal nuclear protein-coding locus markers and their application to osteichthyan phylogenetics with nested PCR. Shen et al. 2012
83.8 Phylogenomic datasets provide both precision and accuracy in estimating the timescale of placental mammal phylogeny. dos Reis et al. 2012
69.8 Molecular and paleontological evidence for a post-Cretaceous origin of rodents. Wu et al. 2012
117.8 Vertebrate time-tree elucidates the biogeographic pattern of a major biotic change around the K-T boundary in Madagascar. Crottini et al. 2012
92.7 Impact of carnivory on human development and evolution revealed by a new unifying model of weaning in mammals. Psouni et al. 2012
92.4 Diversification rates and the latitudinal gradient of diversity in mammals. Soria-Carrasco et al. 2012
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Thanks for the detailed reply, i assume this is called the molecular clock?

Cheers:)

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