selective breeding - genes and myostatin

Beautiful buttock sheep and the legacy of Solid Gold 

Comparing human and sheep genomic sequences reveals six imprinted genes at the callipyge locus 

  The mutation appeared to be a miracle. Sheep breeders in Oklahoma had been selecting for increased muscle in their flock, and in 1983 a lamb was born that developed an overly muscular rump. The breeders named the ram Solid Gold and saved him from slaughter. He went on to sire offspring with the pronounced hindquarters, some of which also passed on the mutation. These sheep became known as callipyge, the name callipyge comes from the Greek for 'beautiful buttocks'. All born since are his descendants.They're Arnold Schwarzenegger-shaped, and their meat's tougher than hell.

This week researchers report the shotgun sequencing and annotation of the callipyge region on sheep chromosome 18. The region contains at least six sheep genes, including four novel sequences. Michel Georges, of the Faculty of Veterinary Medicine at the University of Liege, Belgium, and colleagues used comparative genomics to characterize the region: The raw sheep sequence was analyzed next to human chromosome 14, which contains human versions of sheep genes previously mapped to the callipyge locus.

"It wasn't until the sequence was determined in sheep and then aligned with the human sequence that the four additional genes were pulled out," says Noelle Cockett, of Utah State University and an author of the study. The sequencing was done at Genoscope, Centre National de Séquençage, in Evry, France, and the results appear in Genome Research.

The six sheep genes are expressed in skeletal tissue. "This was important to demonstrate because of the phenotype we are studying," says Georges. His team analyzed tissues from an 8-week-old lamb; signs of callipyge can be detected during the first month of life.

It became clear to breeders in the mid-1980s that callipyge genetics violates just about every known law. Breeders who mated callipyge descendents of Solid Gold got many fewer callipyge animals than they expected. This made no sense to anyone, including scientists.

In 1996, a team led by Cockett and Georges explained what was going on: Only lambs that inherit the callipyge mutation from their father but not their mother develop the trait. All other combinations of normal and callipyge chromosomes result in normal sheep. The researchers named the effect polar over dominance.

The identity of the callipyge mutation still is not known, but a single mutated gene is no longer a plausible explanation for the dramatic effect. Blaming one gene would be straightforward, and nothing about callipyge is straightforward.

"We used to talk about a callipyge gene being responsible for the phenotype, but I've certainly backed away from that," says Cockett. "We now think there's a mutation in a regulatory region that's affecting the expression of these six genes."

The callipyge mutation appears to fall in a DNA sequence governing the activity of multiple genes, the researchers found. "Without knowing the identity of the mutation, we were able to show that the callipyge mutation has effects on the expression of a whole series of genes," says Georges. The findings were published last month in Nature Genetics.

At the University of Liege, Carole Charlier led an analysis of gene expression for four genes in the callipyge region in normal and callipyge sheep. The expression of genes differed among the four genotypes, and gene expression was influenced by two factors: 1) whether a chromosome was normal or callipyge and 2) whether that chromosome was inherited from the mother or the father.

Sheep are only callipygous if their father is; mutant mothers do not pass the trait on. And two big-bottomed sheep will have snake-hipped offspring. How the two mutants cancel each other out is still a mystery.

"Callipyge is really quite fascinating," says Ferguson-Smith. "In a way, it's a shame this happened in sheep, because there are limits to the experiments one can do." Sheep breed only once per year, and flocks are small. Most studies involve relatively few animals compared to what is possible in mice.

The callipyge mutation, whatever it is, may ultimately be more interesting to scientists than the industry. Sheep producers have been cautious about using callipyge genetics because of concerns about the less-than-tender loin chops of the callipyge animal. The loin can be tenderized, but lamb packers have not adopted the practice. In the industry today, callipyge sheep are more of a curiosity than a miracle.

Science tries to block myostatin to prevent muscle loss due to wasting diseases and farmers perform selective breeding to be able to sell double muscled animals, mostly when we talk about this subject we talk about cattle and the specific about the "Belgian blue". Now we posted about sheep, but there are also pigs. Selective breeding is done with birds and chicken. And long ago Adolf Hitler walked the same path to create the Super Human (Übermensch), he had blond blue eyed girls mostly from Scandinavia to pair with his elite soldiers and bring the children up in special schools.

Next freaks of nature wippets with a gen deficit..