inyati13
Well-known member
This came from the American Simmental Association. This write up in more direct that what I have seen elsewhere.
* Developmental Duplication (DD)
A new genetic defect, Developmental Duplication (DD) has been identified. When the gene associated with this condition is paired in a mating the results are either 1) early embryonic death or 2) calves can be born with multiple limbs (polymelia). Polymelia occurs spontaneously in cattle of a variety of breeds as well as sheep, horses, and humans. Other than an increase in the occurrence of mortality associated with dystocia, calves born with these extra limbs often thrive (especially with removal of the limb).
The inheritance of DD appears more complicated than originally thought. The gene is a simple autosomal recessive. However, based on allele frequency, 50% of the expected homozygotes are missing in the population. Originally, it was hypothesized that this could represent embryonic loss of homozygous recessive animals. Recently, a few dozen seemingly normal homozygous recessive animals have been discovered. When animals have the genotype and do not display the phenotype, this is referred to as incomplete penetrance. The cause of incomplete penetrance in DD is unknown but is being researched aggressively. Dr. Beever is examining the DNA of these normal homozygous recessive animals for a potential explanation (for instance, a second gene that interacts with the DD gene) and is planning breeding trials to understand the inheritance better. To further complicate the reporting of genetic defects, it is becoming increasingly clear that all animals are carriers of defective genes. Due to the number of unknowns associated with DD and its inheritance and the increasing number of genetic conditions, the board decided to continue monitoring DD closely but at this time will not add DD to TraitTrac. In the meantime a list of DD test results on Simmental-influenced animals will be made available.
* Developmental Duplication (DD)
A new genetic defect, Developmental Duplication (DD) has been identified. When the gene associated with this condition is paired in a mating the results are either 1) early embryonic death or 2) calves can be born with multiple limbs (polymelia). Polymelia occurs spontaneously in cattle of a variety of breeds as well as sheep, horses, and humans. Other than an increase in the occurrence of mortality associated with dystocia, calves born with these extra limbs often thrive (especially with removal of the limb
The inheritance of DD appears more complicated than originally thought. The gene is a simple autosomal recessive. However, based on allele frequency, 50% of the expected homozygotes are missing in the population. Originally, it was hypothesized that this could represent embryonic loss of homozygous recessive animals. Recently, a few dozen seemingly normal homozygous recessive animals have been discovered. When animals have the genotype and do not display the phenotype, this is referred to as incomplete penetrance. The cause of incomplete penetrance in DD is unknown but is being researched aggressively. Dr. Beever is examining the DNA of these normal homozygous recessive animals for a potential explanation (for instance, a second gene that interacts with the DD gene) and is planning breeding trials to understand the inheritance better. To further complicate the reporting of genetic defects, it is becoming increasingly clear that all animals are carriers of defective genes. Due to the number of unknowns associated with DD and its inheritance and the increasing number of genetic conditions, the board decided to continue monitoring DD closely but at this time will not add DD to TraitTrac. In the meantime a list of DD test results on Simmental-influenced animals will be made available.
