Equine dwarfism is a genetic defect which causes reduction in growth and body deformations, you can also see it as a developmental bones disorder. This disease ends in health restrictions and restricts dramatically the life quality on each dwarf individual.
This is a recessive trait.
The different mutations show up in different phenotypical defects, which also can be combined.
You will find a special gentics topic on the special side of ACAN and Del dwarfism on the right side above the flags.
Misbelief No. 1: The inheritance IS NOT dominant! Would it be dominant only one allele passed to the foal would show up in dwarfism. But this is not true. A rezessive inheritance will only show up when two alleles (one by each parents) are passed and will show up in a trait (in this case dwarfism). If you have a dwarf foal both parents inherited a dwarfism mutation on that foal.
Rezessive alleles only show up in a phenotype when they are homozygous. In reverse that means if a horse carries only one allele (heterozygous) you can see it on its phenotype, you call this horse a carrier because it can inherit this allele.
Do you breed carriers (see table above) you can get normal/healthy foals, carrier foals but also dwarf foals.
The danger is that a recessive allele can be inheritet through generations without notice. And one day -BOOM- you will have a dwarf foal.
Misbelief No. 2: Stallions were to be said to inherit dwarfism. This is not true. Now it is proven that dwarfism is a rezessive genetic disease and both parents need to inherit it for getting a dwarf foal. Equine dwarfism IS NOT linked to a special sex.
The above table shows mating carriers. As mentioned above here you can breed normal/healthy foals, carrier foals and dwarf foals.
Misbelief No. 3: Normal looking horses will never breed dwarf foals. That´s proven not true! Also "normal" and "healthy" looking horses can be carrier. Mating these can produce dwarf foals. This recessive trait can be inherited over generations without notice.