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What Does it Mean to be a Carrier, Free, or Affected for Different Genetic Defects?

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Many genetic defects are simple recessive traits, meaning it takes two bad alleles (versions of a gene) to see the condition. If an animal is tested free (for instance DDF means tested free for DD), the animal does not have one of these defective alleles. If the animal is a carrier (DDC) then that animal has one normal copy and one defective copy of the gene. If an animal is affected (DDA) then both copies of the gene are defective. Typically we would expect these affected animals to show the signs (phenotype) for that genetic condition. The only way to get affected animals is to mate a carrier bull to a carrier dam. In carrier to carrier matings, we expect 25% of the progeny to be free, 50% to be carriers and 25% to be affected.

In the case of DD, some animals have both defective copies of the gene but don’t show any sign of the genetic condition (this is called incomplete penetrance). With incomplete penetrance, some other factor is needed for the phenotype to display. This trigger may be environmental (nutritional, stress, etc.) or genetic (a second gene involved in the pathway).

 
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Down to the Genes Series

Top Tips for Easy, Efficient DNA Testing

October 31, 2020 DNA
As we head into fall, weaning, and long days working cattle, ASA’s DNA department wants to share some of our top tips for easy, efficient DNA testing. Preparation is key, and we want our membership to have the tools to successfully test animals and take advantage of DNA technology. ➔ The most straightforward, error-free way to order DNA testing is to go to simmental.org, click on DNA Testing,…

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