Gene Marker Results

 

Gene Marker results are displayed on the web in two parts - a gene marker code and a test result.

 

1. Gene marker code

            M1-  GeneStar Marbling 1

            M2-  GeneStar Marbling 2

            M3-  GeneStar Marbling 3

            M4-  GeneStar Marbling 4

            T1-  GeneStar Tenderness 1

            T2-  GeneStar Tenderness 2

            T3-  GeneStar Tenderness 3

            T4-  GeneStar Tenderness 4

            FE1-  GeneStar Feed Efficiency 1

            FE2-  GeneStar Feed Efficiency 2

            FE3-  GeneStar Feed Efficiency 3

            FE4-  GeneStar Feed Efficiency 4

 

2. Test result

0 indicates the animal carries zero copies of the favourable form of the gene.

1 indicates the animal carries one copy of the favourable form of the gene.

2 indicates the animal carries two copies of the favourable form of the gene.

 

For example,  M3-2  indicates a GeneStar marbling 3 test with a result of 2 favourable forms of the gene.

 

Most animals listed with a gene marker result have had their DNA tested and this is described in the result line – for example:  “Tested Tenderness (T1-2,T2-1)”.  However, some animals may have a “Derived” result because both parents have been tested and their specific results enable us to predict the gene forms of their progeny (see Predicting Progeny below).  In many cases, however, it is not possible to predict the gene forms of the progeny even when both parents have been tested.

 

Click on the logo for more information on their DNA markers and other commercial products.

 

 

Gene Markers

 

Gene markers exploit major genes that show a favourable influence on traits of interest.  The effect of the major gene on the trait of interest can vary.  The larger the size of the effect, the more useful the marker is in describing better performance animals in your herd for that trait.  You need to talk to the relevant DNA laboratory about the size of the effect of the gene identified by the gene marker in relation to the overall variation found in that trait within your breed. 

 

DNA marker tests are evolving and new markers are under continual development. Therefore, animals may not have results for all markers as:

 

DNA marker results are supplied on a voluntary basis to the breed societies. 

 

 

DNA, Genes and Inheritance

 

DNA contains the genetic blueprint of an animal. Within the DNA, there are small segments called genes.  These genes relate to specific functions within the animal (assembling proteins from amino acids).  These functions may impact on the expression of traits (eg growth to 400 days of age) for that animal.  The expression of traits by an animal is usually a combination of the effects of many genes operating within the animal, rather than a single gene.  Some genes may have more of an impact on a trait (ie a major gene) than other genes.  That is, not all genes have the same effect on the trait of interest.  Genes may also affect more than one trait – hence the visual relationships we tend to see between say growth to 400 days and weight at maturity.  Cattle DNA is likely to have some tens of thousands of genes affecting traits to varying degrees.

 

There are also environmental influences that will affect the trait as well.  For example, actual 400 day weight will also be influenced by the amount and quality of fodder available, animal health, etc. The effect of these environmental influences on a trait may be greater than the genetic influence.  Indeed, some traits may not be expressed until the environment is favourable.  For example, marbling may not be expressed if animal nutrition is poor.

 

Genes occur in pairs. Animals get one copy of a gene from its sire and one copy from its dam.  The resulting pair of genes combine to give the overall effect on the trait of interest for the calf.  

 

There are usually two forms of a gene.  One form of a gene may be more favourable towards the trait of interest than the other form of the gene.  Each form of the gene may be expressed independently on the desired trait, in which case the effect of the gene forms is additive. Conversely, one form of a gene may mask the effect of the other form – this is called dominance.

 

If we consider two forms of a gene as “B” and “b”.  There are 3 possible combinations of the gene pair viz: “BB”,  “Bb” and  “bb”. 

 

If the “B” form of the gene is favourable on the trait of interest and the effects of the gene forms are additive, then it is expected that animals with the “BB” genes will perform better for the trait of interest than the “Bb” animals. Similarly the “Bb” animals will perform better than the “bb” animals.  The genes identified in the GeneStar Tenderness markers are of this type. Relating this example to the T1 marker results, the “BB” form would get a result of “T1-2”, the “Bb” form would be “T1-1” and the “bb” form would be “T1-0”.

 

However, if we looked at a dominant gene form “R” and its non-dominant (recessive) form “r”, then we still get the same possible combinations of pairs (RR, Rr and rr) - but get different effects.  Where a gene form is dominant, it hides the effect of its recessive form so that “RR” and “Rr” will show one result and “rr” will show another. An example of this is black and red coat colour in Angus cattle.  Animals with the dominant genes (ie “RR” and “Rr”) have black coats while the red coat animals only have the recessive genes (“rr”).  The “Rr” animal is black but is described as a “red carrier”.

 

 

Predicting progeny

 

Knowing the results of the gene markers for a particular marker for both parents, you can predict the likely gene form of their progeny for that marker.  The easiest way to describe how to do this is to use a technique called Punnet Squares. 

 

If we assume the favourable form of the gene is “B” and the less favourable form is “b”, then the gene marker results can be interpreted as:

Gene Marker Result

0

1

2

Gene pairs (using “B” and “b”)

bb

Bb

BB

 

Hence if we had an animal with a marker result of T3-1 its gene pair would be represented as “Bb”.

 

By relating the gene marker result to its gene pair in the table above, we can then put the gene pair code for the sire at the top of a 2x2 table and the gene pair code for the dam on the left hand side.  By combining one gene form from the sire with one gene form from the dam, we can easily see the possible combinations of the genes that the progeny may get:

 

 

 

Sire

 

 

genes

B

b

 

Dam

B

BB

Bb

 

b

bB

bb

 

This indicates that a Bb sire mated to a Bb dam will on average have:

BB progeny 25% of the time

Bb progeny 50% of the time (Bb = bB)

bb progeny 25% of the time

 

This technique is called Punnet Squares.

 

Following is a series of Punnet Squares with all possible combinations of gene pairs with a 0,1 and 2 result for both parents.

 

 

 

Sire (2)

 

Sire (1)

 

Sire (0)

 

genes

B

B

 

B

b

 

b

b

Dam

B

BB (2)

BB (2)

 

BB (2)

Bb (1)

 

Bb (1)

Bb (1)

(2)

B

BB (2)

BB (2)

 

BB (2)

Bb (1)

 

Bb (1)

Bb (1)

 

 

 

 

 

 

 

 

 

 

Dam

B

BB (2)

BB (2)

 

BB (2)

Bb (1)

 

Bb (1)

Bb (1)

(1)

b

Bb (1)

Bb (1)

 

Bb (1)

bb (0)

 

bb (0)

bb (0)

 

 

 

 

 

 

 

 

 

 

Dam

b

Bb (1)

Bb (1)

 

Bb (1)

bb (0)

 

bb (0)

bb (0)

(0)

b

Bb (1)

Bb (1)

 

Bb (1)

bb (0)

 

bb (0)

bb (0)

Note: Numbers in brackets are the number of favourable gene forms.  Bb is same as bB.

 

 

Note that where both parents only have one form of the gene (BB or bb), we can derive the gene pair for the progeny based on the information of the parents.  That is:

 

However, other combinations of parent gene pairs give multiple options for the progeny, in which case  we cannot accurately determine what gene pairs a particular progeny is, if based solely on its parents’ gene pairs.

 

You need to look at each marker independently (ie you cannot mix the results of different makers in the same punnet square). Hence you need to do a separate punnet square for each marker.  As more markers become available, it is more difficult to optimise the results for all markers as you need to allow for all the combinations of outcomes for each marker.

 

When you have parents with results on multiple markers, you can multiple the frequency of the desired outcome for each marker together to get an overall expectation of getting progeny with an overall desired outcome for all markers. 

 

For example, if a sire and dam both have a marbling result of M1-1 and M2-1, then using the punnet squares table above, the chance of getting progeny with the gene pair combinations for each marker are:

M1-2   BB progeny 1 in 4 (¼)                      M2-2   BB progeny 1 in 4 (¼)

M1-1   Bb progeny 2 in 4 (½)                       M2-1   Bb progeny 2 in 4 (½)

M1-0   bb progeny 1 in 4 (¼)                       M2-0   bb progeny 1 in 4 (¼)

 

Therefore, there is a:

(¼ x ¼) = 1/16 chance of getting progeny with a result of M1-2 and M2-2,

(¼ x ¼) = 1/16 chance of getting progeny with a result of M1-0 and M2-0,

(½ x ½) =  ¼  chance of getting progeny with a result of M1-1 and M2-1,

(¼ x ½) =  1/8 chance of getting progeny with a result of M1-0 and M2-1,

etc …

 

You can also consider getting progeny with, say, at least one favourable form of the gene for both markers. Using the same sire and dam as an example:

(¼ x ¼) = 1/16 chance of getting progeny with a result of M1-2 and M2-2,

(¼ x ½) = 2/16 chance of getting progeny with a result of M1-2 and M2-1,

(½ x ¼) = 2/16 chance of getting progeny with a result of M1-1 and M2-2,

            add these fractions together to give:

 5/16 chance of getting progeny with at least one favourable form of the gene for both markers.

 

The same concepts apply for more markers as well, although the calculations get more tedious as you add more markers.