Rapid Selection, Overdominance & Disease As A Side Effect Of Adaptation: Domesticated Cattle And Muscular Hypertrophy
In another example of overdominance resulting from quantitative trait selection, several breeds of cattle (such as Belgian Blue and South Devon) have polymorphic frequencies of a mutation of the myostatin gene that caused muscular hypertrophy (Wiener, 2002). This mutation has a frequency of 37% in the South Devon breed, where it significantly increases muscle mass but increases calving difficulty. The fact that this mutation has not gone to fixation, even though selection favours heterozygotes, suggests that it is overdominant.
Wiener, P., Smith, J. A., Lewis, A. M., Woolliams, J. A. & Williams, J. L. (2002) Muscle-related traits in cattle: the role of the myostatin gene in the South Devon Breed. Genetic Selection and Evolution 34, 221–232.
Quoted on Sun May 20th, 2012