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:
- their DNA tests may have been done prior to
the release of “new” markers; or
- the results of the test were inconclusive.
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:
- BB (2)
x BB (2) only gives BB (2) progeny
- BB (2)
x bb (0) only gives Bb (1) progeny
- bb
(0) x bb (0) only
gives bb (0) progeny
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.