Is a horse's height and roaring linked to a genetic component?

"...Researchers have noted a positive correlation between Thoroughbred racehorse height (and leg length) with earnings. But breeding pressure to instill the 'tall' gene might have created unintended consequences. Scientists have now identified a link between height and the respiratory condition recurrent laryngeal neuropathy (RLN, or 'roaring) in Thoroughbred racehorses and in draft horses. In a 2014 study out of Michigan State University, the authors -demonstrated 'a significant association of RLN with the LCORL /NCAPG locus (the position of a gene on a chromosome) on equine chromosome 3 previously shown to affect body size in horses.' This same location is known to have a significant effect on Thoroughbred withers height.

'Genes are strung along the chromosome like pearls on a necklace,' says Brooks, reflecting on SNP proximity. 'Those that are nearby to one another will tend to stay together and aren't often separated by the process of recombination,' which produces offspring with combinations of traits different from those found in either parent.

'If selective breeding increases the frequency of the tall gene, and if it sits on the same chromosome as the neuron--affecting gene, then there may be a simultaneous increase in both frequency of height and for a disease like roaring,' she says.

More research is needed to determine the RLN and height genes' actual proximity or if they are the same gene performing two unique functions, says Brooks. ..."