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12 fascinating facts about DNA

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Subject: Facts about DNA that genetics labs may not tell you
Author: Donna Grace Vickery, homestead.cattle.assn@gmail.com

Geneticists may not be able to claim some of the things I claim as "facts" in this short report ... because my list of "facts" about DNA could be disproven in rare, freak, solitary cases. In fact, that is what a mutation itself is: a changed or broken sequence in DNA, which goes against the former rules or facts (that we often label as "wild type" in livestock genetics). In some cases, history, registries, breeding programs, profits and even livelihoods, were built on unclear understanding of genetics, before we knew more about them. For many reasons, what we have learned, is not openly discussed, for fear of blowback, therefore, many of us still do not hear much about today's known DNA "facts". This article is intended to set a foundation understanding about how DNA mutations work, and what they can tell us about the animals standing in front of us, and about that animal's ancestry. This information illustrates how mutations over decades and centuries provide reasonable doubt or proof of relationships between breeds, their origins, history and development.

  1. Genetic diseases in cattle are tissue specific viz; skeletal, central nervous system, blood, skin /hair, muscle or ophthalmic.

  2. Genetic disorders and diseases are caused by inherited mutatations; which are damaged genes or chromosomes.

  3. In 2016, there were 130 Mendelian traits with known causal mutations in 117 cattle genes. We find more every year.

  4. Genetic mutations do not all cause what we term disorders or disease (for example polled mutations).

  5. Genetic mutations are very common* and we now understand that multiple mutations probably exist in all living animals. The possibility of how many mutations may occur in any one population over time, is practically infinite. Perhaps that is comparable to how many different places lightening can strike over time. It is said that lightening strikes earth about 8 million times per day.

  6. On the opposite end of the spectrum, is the probability of the exact same mutation happening more than once in the same breed or population of animals over time; which is practically nil. The possibility of that occuring would be much lower than the chance of lightening striking twice in the same spot. It might be more comparable to finding 2 unrelated people accused of a crime with identical fingerprints. When I really want to put this in perspective, I say the likelihood of the same exact mutation happening more than once in the same breed or population of animals over time would be less than the chance of me winning the lottery.

  7. For all reasonable intents & purposes, if the exact same genetic mutation is found in 2 different animals of the same species, they are related. It is reasonable to assume, and important to understand that 2 animals with the same exact mutation will both trace back to one single ancestor that the mutation originally occurred in, and was passed down from. That is why particular genetic mutations are found in breeds that share history, or only in specific breeds, or only in certain bloodlines, depending upon how long ago the mutation occurred and how widely it has spread. It may have occured (or been discovered) a year ago, or it may have occured centuries ago in bovine history. This is one way the history of animal breeds can be documented.

  8. Many genetic mutations are recessive. Many recessive mutations are undesirable. Most of them (if inherited as homozygous) probably result in spontaneous abortions, or do not survive into breeding age animals. Undesirable mutations that are dominant or semi-dominant do not last long in a breed if the trait is something that mankind or nature selects against. Some mutations are surviveable over generations, or even benign. Occasionally a few are even beneficial (to nature or mankind). Mutations, genetic drift, natural selection and migration, are some of the basic mechanisms of evolution, and help populations survive environmental changes, as well as develop breeds under selection pressure.

  9. Some genetic conditions are markers (closely linked) for economically important or desirable traits. Those can be the quickest to spread in a population. For example, desirable hair for club calves may result from alleles located close on the gene to the PHA disease mutation, which initially led to the increase of PHA among Maine Anjou influenced club calf cattle. There are many other examples of this in breeds of cattle.

  10. There can be a great number of different mutations that result in the same identical disease. For example, there are several different mutations (probably at least a half dozen) that cause what we know as the bulldog chondrodysplasia form of dwarfism in cattle. We have isolated at least a dozen myostatin mutations that result in double muscling. And yes, if 2 animals test positive (to the same identical test for the same identical mutation) then, those 2 animals are related, whether recently, or long ago.

  11. Each different mutation requires its own specific DNA test to identify it (even if the disease or condition they cause is identical). When you test an animal for bulldog dwarfism, it takes a separate test for each known mutation that causes that disease.

  12. Genomic technology is ever-evolving. Before making any financial decisions, such as choosing a breed, or implementing a DNA testing program in your cattle herd, or signing up for all the DNA tests recommended by your registry, inform yourself. First, learn your livestock's heritage. Know what breeds and what bloodlines are in your animals' pedigrees. Check for the latest research news, lab tests, products and news. If you are not currently testing it may be prudent to collect DNA samples (e.g. tail hair) on important animals in your herd (e.g. A.I. sires, herd bulls, donor cows, or your best replacement lines of cows) and store them for potential future research if anything crops up later in your herd.

mutations of DNAGenotyping is a process whereby cattle's DNA (extracted from tissue; in hair roots, blood or semen) is analyzed to identify genetic traits known to affect them. Before (about 1990) DNA testing, a calf's genetic merit was predicted from its parents' expected progeny difference averages (EPDs). Now, with genotyping, cattle owners can learn much more about their calves, immediately & accurately. This can improve profits, increase the herd's value, and contribute to faster overall breed improvement.

Accuracy: DNA tests are 100% accurate. That is the theory. However, it is generally accepted that in the absence of genotyping for parentage, 5% of cattle pedigrees may be incorrectly recorded in older generations..

Should cattle tested to carry a genetic defect be culled?

Short Answer #1: Is the mutation advantageous? No.
Short Answer #2: Is the mutation recessive? No.
Short Answer #3: Is the animal genetically valuable? No, unless:
Short Answer #4: Is the mutation (semi- or) dominant--AND deleterious? Yes.


Haplotypes Affecting Fertility and their Impact on Dairy Cattle Breeding Programs
*"Times have changed, and today we recognize that ...inherited conditions are not rare anomalies that occur once in a decade in a handful of genetically unfit animals. Armed with a much deeper understanding of the genomes of cattle and other food animal species, scientists now believe that it is likely that every individual carries several genes that, if expressed in homozygous form, would lead to a severely impaired or lethal phenotype."
Dr. Kent Weigel, Professor & Chair, Dep't of Dairy Science, U of WI, Madison; Aug, 2011.

AgriGenomics Mansfield, Illinois
Biogenetic Services, Brookings, South Dakota
Neogen, GeneSeek®, Igenity, SeekSire, Neogen Genomics®, Lansing Michigan
Genetic Visions, Middleton, Wisconsin
MMI Genomics, Davis, California
Pfizer Animal Genetics, Harahan, Louisiana
Reprotec, Tucson, Arizona
UC Davis Veterinary Genetics Lab (VGL), Davis, California
Zoetis Genetics (formerly Pfizer Animal Health), Kalamazoo, Michigan
The American Grey Steppe Cattle Association, Borntograze.com
Veterinary Medicine (Eleventh Edition), 2017
Dr. Tony Knight, CSU)
https://www.researchgate.net/publication/273204232_Genetic_diseases_of_cattle (2010)
Genetic Defects • www.eBEEF.org • 2014-9
From Big to Small to Big to Small: A 3-part Pictorial History of Cattle Type Changes Over the Years, by Harlan Ritchie
and too many more to list...


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