White (horse)

A Dominant white horse receives its completely white color by leucism, that is, the melanocytes, the cells that produce the dyes are not reached in the skin due to a mutation.

Appearance

A horse with Dominant white color is from birth to the entire body snow white fur and pink skin. Only at the ears, in the mane or tail can in some colored hairs occur. The horse eyes are brown.

Genetics

It was assumed that there is a white gene (W), which has a dominant mode of inheritance. It has now been found, however, that several different mutations of the KIT locus lead to dominant white color. It is thus a form of leucism.

Some of these W - genes are in their homozygous expression ( WW) in the early embryonic lethal. That is, they lead to a miscarriage at this time. In other W genes is not known what influence the homozygous expression.

In rare cases it may happen that the gene W in heterozygous form is not fully expresses, but produces a spotting that looks like a Sabinoscheckung.

From heterozygous dominant white horses no health problems are known.

The same gene is at Tobiano, mutated in the color changer and the Sabinoscheckung. In the genes to ( no Tobianoscheckung ), w ( no Dominant white color), rn ( no Stichelhaarigkeit ) and sbn ( no Sabinoscheckung ) so are in each case were the same gene - namely, the normal color without white spots - while To ( Tobianoscheckung ), Sbn1 (which is a previously known gene for Sabinoscheckung ), Rn ( Stichelhaarigkeit ) and W (dominant white color) are different alleles of the same gene. If ( the gene therefore has twice) a horse for one of these four genes is homozygous, it can have none of the other two genes. If it is not homozygous, it can have at most two of these investments. Nearby on the same chromosome is the extension locus of the horse so that the chestnut color is often passed through several generations in conjunction with one of these genes.

W genes of different races

Freiberger

In Freiberger horses a mutation of the KIT locus occurs, caused by a nonsense mutation in exon 15 of the gene that causes the KIT protein is only partially synthesized because of premature stop codons. Heterozygous horses that have a mutated and a healthy allele of the gene mutated KIT protein is only about half as likely as the healthy. This is due to mechanisms that serve to degrade damaged proteins or to prevent their synthesis. This mutation is likely if it is present homozygous lethal at an early embryonic stage.

The mutation can be traced back to the white mare Cigale, who was born in 1957.

Arab

Three almost white Arabs had another nonsense mutation in exon 4 of the KIT locus. This mutation is likely if it is present homozygous lethal at an early embryonic stage.

Camarillo White Horse

Six horses of the breed Camarillo White Horse had a missense mutation in exon 12 of the KIT locus. It goes back to the founding stallion of the breed Sultan, who was born in 1912.

Thoroughbred

Five white English thoroughbred had another missense mutation in exon 13 of the KIT locus. According to the pedigrees of English Thoroughbreds, there are several families in which a dominant white mutation has occurred independently.

More genes

2009 were discovered for dominant white color in the KIT locus in English Thoroughbreds, Iceland ponies, Holsteiners, Quarter Horses and southern German cold blood seven other genes.

Possible confusion

• Cremello, Perlino, Smoky Cream: Twice differ by the Cream gene brightened horses from the Dominant White horse by her blue eyes. The coat has a slightly golden or silver shimmer and is not as white as snow.
• Mold: has dark skin
• Maximum piebald: Depending on the check - gene different eye color, otherwise Dominant White Horse