Glossary of Genetic Terms

Basic Genetics Terminology

Gene – A hereditary unit consisting of a sequence of DNA that occupies a specific location on a chromosome that is transmitted from one generation to the next. (The American Heritage Dictionary of the English Language, 5th Edition)

Allele – One of two or more alternative forms of a gene that can have the same place on a chromosome and are responsible for alternative traits, i.e. horned/polled. (The American Heritage Dictionary of the English Language, 5th Edition)

Homozygous - having two identical gene/alleles. The gene/allele received from their Dam and Sire were the same. We will use "Horned/Polled" as an example: If the Sire passed on the polled gene, and the dam also passed on the polled gene, the calf would be Homozygous Polled and could not have horned calves. (Pc/Pc)

Heterozygous - having two different gene/alleles. The gene/alleles received from their Dam and Sire were different. Example: If the Dam passed a polled gene (Pc) to the offspring, but the sire passed on a horned gene, the offspring would have 1 gene for horns and 1 gene for polled. (Pc/H) The calf would be Heterozygous. Because the polled gene is dominant (see below) the calf will not be horned but may have horned offspring.

Genotype - a "screenshot" of the Genetic "fingerprint" of the animal. We use that to Parent Qualify.

Parent Qualification/Verification - Uses the Genotype of the Sire and the Dam to determine if it is possible these parents produced this offspring. It does NOT guarantee that these are the parents, only that there is nothing to disqualify the sire and the dam.

Obligate/Obligation - Obligate status is when you have tested the Sire and Dam, and their Parent Qualified offspring, only has 1 possible genetic outcome due to the sire’s and dam’s gene/allele.

Example 1 - An A2/A2 Cow bred to an A2/A2 Bull, the offspring can only be A2/A2.

Example 2 - An A1/A1 Cow bred to an A2/A2 Bull, the offspring can only be A1/A2 because the calf inherits one A1 gene from the dam and 1 A2 gene from the sire. Obligation can save you big money.

The PDCA will accept obligation status on all traits that qualify.

Phenotype - the composition of your Dexter that can be seen/touched/measured often referred to as Conformation of the Dexter, such as hindquarters, head, legs, feet, udder, topline (back) etc.

Dominant -A dominant gene will block or override the expression of the recessive gene. An example of this is the polled gene. If an animal carries one copy of the polled gene the animal will not have horns, even if it also carries a horned gene.

Recessive - can only be expressed if the dominant gene is not inherited. For example: For a Dexter to be horned, no Polled gene can be present. The animal must be homozygous horned (H/H).

Beef Genetics Terminology

Included in Igentity Beef and Neogen Tenderness/Leptin Panel

Tenderness (TEND) - Genetic potential for beef tenderness based on Warner-Bratzler Shear Force. Trait is scored in the Igenity Beef and the Tenderness/Leptin Test. The scoring is a 1 through 10, the higher the number the more tender the beef. The score for tenderness is based on whether or not the animals carries Caplain316, Calpain 4751, and CAST.

Tenderness - Calpain316 - This gene is not common in the Dexter Breed. It is there, just harder to find. Calpain works to break down muscle fiber and is a predictor of tenderness. Alleles each explain from 0.4% to 2% of tenderness variation across breeds. When you run the Tenderness/Leptin Test from Neogen, there are 3 possible outcomes for this test. CC, CG, GG. The ‘C’ allele is associated with more tender meat.

Tenderness - Calpain4751 - This gene is easier to find and makes a more significant impact to the overall score. Three potential outcomes from this test are CC, CT, TT. The ‘C’ allele is associated with more tender meat.

Tenderness CAST - Calpastatin is an inhibitor of Calpain. When testing through Neogen using the Tenderness/Leptin test, three outcomes are possible. CC, CG, GG. The ‘C’ allele is associated with more tender meat. Leptin - Leptin is a fat-metabolism hormone with a mild effect on fat deposition. The three possible outcomes are TT, CT, CC. Leaner cattle carry allele C and more marbled cattle carry the allele T.

Dairy Genetics Terminology

Casein - is the largest group of proteins in milk, making up 80% of the total protein content. There are several types of casein in milk. Beta casein is the second most prevalent and exists in at least 13 different forms. (https://www.healthline.com/nutrition/a1-vs-a2-milk) The types most commonly tested for are: A2 Beta casein, Kappa casein and AB Beta casein.

A2 Beta casein - Test results for A2 Beta casein are grouped into... A1/A1, A1/A2 and A2/A2. Most milk contains A1 and A2 Beta casein, however, if the milk is sold as A2 milk it only contains A2 Beta casein. There are some studies which suggest that A2 Beta casein milk may be more digestible for people who have difficulty digesting dairy.

Kappa casein – Important for cheese making. The gene responsible for Kappa casein production in cows, CSN3, exhibits variations, leading to different forms of the protein. Several forms of Kappa casein have been identified, with A, B, and E being the most common variants. These genetic variants combine to form different genotypes in cows, such as AA, AB, BB, AE, BE, and EE. Each genotype produces a slightly different form of Kappa casein, which directly impacts the composition and coagulation properties of milk. For example, cows with the BB genotype generally produce milk with higher fat and protein. This genotype is also associated with more favorable milk coagulation properties. Milk from cows with the BB genotype tends to clot more quickly and forms a firmer curd compared to milk from AA or AB genotypes. Conversely, milk from cows with the EE genotype may not clot effectively for cheesemaking, making it less desirable for processors. These differences in clotting time and curd firmness are important for dairy processing. (https://biologyinsights.com/kappa-caseins-role-in-milk-quality-and-cheese-yield/)

AB Beta casein - A protein associated with improved cheese making. AB Beta casein refers to a genetic variant of the Beta casein protein found in milk, where the individual carries both the A1 and A2 alleles. A1 and A2 Beta casein are two different forms of the same protein, differing by a single amino acid at position 67 of the protein chain. This single amino acid difference can affect how easily the milk is digested and whether it triggers sensitivities in some individuals. Three outcomes are possible in this test. (B/B, A/B, and A/A). B/B is most favorable; A/B is intermediate; A/A is least favorable.

Beta Lactoglobulin – A protein found in the liquid portion of milk, known as whey. This protein is widely recognized for its presence in the milk of cows, sheep and goats; it has a significant effect on cheese yield. Three outcomes are possible (A/A, A/B and B/B); B/B is most favorable; A/B is intermediate; A/A is least favorable. (https://biologyinsights.com/what-is-beta-lactoglobulin-function-and-allergy/)