Morgan: Dr. Saltz and I read Lande and Arnold’s paper titled "The Measurement of Selection on Correlated Characters" in a class we took together in graduate school. This paper had a really important impact on the field of evolutionary biology, because it made the prediction that traits that are correlated may not always be able to evolve independently. When the paper was written (in 1983), no organism’s genome had been fully sequenced. Now, 30 years later, it is common to use genomics to investigate trait correlations. Dr. Saltz and I wondered what new information had been learned from these techniques. Had any of this new information changed scientific understanding of trait correlations?

Julia: Our next update will be due in 2043!

College of Science: Why is it important to understand the genetic basis of trait correlations? How has new technology to sequence genomes changed the study of trait correlations?

Morgan: Before DNA sequencing, scientists could observe that a given set of traits were correlated, but they couldn't identify the actual DNA sequence differences that were causing variation in those traits. Now that whole genome sequencing is relatively common, scientists have been able to identify the actual genes and regions of the genome where variation in DNA sequences leads to variation in the traits they're studying. This has led to the discovery of a number of surprising examples where variation in a single gene produces variation in multiple (sometimes seemingly unrelated) traits.

College of Science: What is your favorite trait correlation in a species?

Morgan: My favorite example (which I learned from Dr. Saltz) is the T gene in dogs. There are 17 dog breeds that have naturally short tails. The version of the T gene that produces short tails has a mutation that disrupts the ability of the T protein to bind to DNA. Dog breeds with short tails never have two copies of this gene, which suggests that any dog that inherits two copies of this gene (1/4 of a typical litter in these breeds) must die in utero. Thus, a version of a gene that was favored by breeders also has a critical effect on the animal's viability.