Humans have bred dogs to produce tremendous variety. But a new study reports that the physical variance among dog breeds is determined by differences in only about seven genetic regions. These seven locations in the dog genome explain about 80 percent of the differences in height and weight among breeds, said Carlos Bustamante, a geneticist at Stanford University and one of the study’s authors. The findings, published in Public Library of Science-Biology, are a result of what is the largest genotyping of dogs to date, involving more than 1,000 dogs and 80 breeds.

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The Breeder’s equation R = h 2 S R = The response to selection h 2 = heritability (in the narrow sense) S = the selection differential

The Breeder’s equation R = h 2 S R = The response to selection h 2 = heritability (in the narrow sense) S = the selection differential 3.5 Mean of population 5.5 Mean of selected individuals

The Breeder’s equation R = h 2 S R = The response to selection h 2 = heritability (in the narrow sense) S = the selection differential 3.5 Mean of population 5.5 Mean of selected individuals S = a – b = 2

How do we find heritability? Controlled experiments h 2 = slope of the best fit line Heritability (in the narrow sense) reflects the degree to which offspring resemble their parents. Or The degree to which variation in the population (offspring) is due to variation in genes (parents).

The Breeder’s equation R = h 2 S R = The response to selection h 2 = heritability (in the narrow sense) S = the selection differential 3.5 Mean of population (b) 5.5 Mean of selected individuals (a) S = a – b = 2 if h 2 = 0.5, what is the response to selection?

Original population mean Mean of offspring If h 2 = 0.5 R Response to selection