Now the definition of (narrow sense) heritability used by population geneticists is different from the commonly-understood definition. When most people think of "heritability" they think of passing something down from parents to offspring. But population geneticists define heritability as the ratio of the variance of a trait due to genetics to the variance of the trait. (Some of you may remember "variance" from a statistics course.) Heritability tells us how much of a trait is due to genetics and how much to environment, and is a number between 0 and 1.
For example the heritability of height in humans is estimated to be 0.8, meaning that most of the cause of height is genetic, but the rest (0.2) is caused by environmental factors (nutrition, etc). Another example is hip dysplasia in dogs. Here the heritability is much lower. I calculate that the heritability of hip dysplasia in Norwich terriers is 0.36. This is in line with papers that I have read for heritability of hip dysplasia for dogs in general and also for specific breeds. This explains why it is so hard to change hip dysplasia results for a population of dogs - only a little of the cause is due to genetics with most due to environment. (Environment includes measurement errors.)
I have been playing around with estimating heritability of NTUAS using the reports that people have sent me, see
http://shakspernorwich.net/pedigreedb/details/uasreports.html
I calculate that the heritability of NTUAS is 0.72, meaning that most of the heritability is due to genetics. I want to emphasize that this is a preliminary result, as I only have a small amount of data, and subject to change as I get more data. But if it is roughly accurate, it means that a little selection pressure will have a big effect on improving the airways of our dogs.
4 Feb 2021