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GENETICS OVERVIEW

There are three important things that need to be kept in mind:

1. The Breedplan figures are not a description of the animal itself, but a prediction of what its calves are likely to be terms of those characteristics that are measured by Breedplan. The comparison to be made is with the current average values for that breed.

2. The figures represent probabilities and not certainties and are arrived at by statistical analysis. The term “statistics” frightens many people, but properly applied are the reason why Casino operators flourish at the expense of their patrons.

3. Breedplan figures represent only those characteristics such as weight, testicular circumference, fat depth and eye muscle area that can be objectively measured. Other characteristics such as structural correctness and coat colour [if that’s important to you] are assessed by eye alone.

Another matter that deserves emphasis is that differences in EBVs are small. A bull may have a 600 day weight EBV of say 30 kilograms above average, but in animals that could weigh anything up to 800 kilograms such a difference could be completely masked by environmental effects including feeding.

Such differences, although small, do accumulate over the generations if they are selected for as shown in those graphs that demonstrate how the breed average has improved progressively over the years. All desirable characteristics need to be selected for if the female herd is to continue to make progress.

You can learn a good deal about a bull by looking at it including his size, fat cover, confirmation, structural correctness, butt shape, coat colour, markings and overall eye appeal and these qualities often represent about all the prospective purchaser takes into consideration in making a decision.

However, it could be very useful to know other data including the bull’s date of birth, his weight at different ages and his ranking amongst other bulls of the same age reared under identical conditions. It would also be informative to know his birth weight and how he scanned for fat depth, eye muscle area and marbling. Additional information is often also available on his sire, dam and other close relatives. By the time all this information becomes available, evaluation of the bull becomes increasingly complex and this is when help from an expert statistician is required. If this sounds familiar it is because you are starting to look more closely at the way in which Breedplan operates.

Chance enters into our considerations in two ways. The first concerns the accuracy of the EBV’s themselves. It has been said that statistics relies on the law of large numbers and the more the data available the more reliable the conclusions. This is why animals with large numbers of calves recorded and links to animals in other herds by AI have higher accuracies than those that have yet to have calves or that have few relatives on record.

The second way in which chance plays a part concerns heritability. This is the probability that an animal will resemble its parents and lies anywhere between 0 percent (the character in question is not inherited) and 100 percent (for example, the white face in Herefords]. In practice the heritability of most traits ranges between 10 percent [for fertility] and 70 percent [for carcase eye muscle area] so that obviously greater progress is going to be made in selecting for muscling than selecting for fertility. Data of this kind does not rely on theoretical considerations but is derived from actual measurements of the trait in large numbers of animals.

GENETICS AND THE ENVIRONMENT

Genes, consisting of DNA, are strung out along the chromosomes (coloured bodies) which are found in the nucleus of all cells and take up certain dyes, hence their name.

They occur in identical pairs except for the Y chromosome which is confined to the male sex and matched with an X chromosome whereas the female has a pair of X chromosomes.

The nucleus of all body cells irrespective of their function has an identical set of chromosomes which is peculiar to that individual unless it happens to be a twin. When the sex cells, sperms and ova, are formed each receives only one of each pair and they are shuffled around in such a way that no two sex cells are identical from which it follows that the results of the union of two such cells is an unique individual unless splitting takes place in development resulting in identical twins.

The interaction between the genes (genotype) and the environment in which it is raised give rise to the animal you see (phenotype). One can liken it to the interaction between the seed and the soil which will determine how well a plant flourishes. Unlike animals, however, cloning in plants is a simple process and has been practised for centuries. By means of cutting or by budding, grafting and layering, plants can be propagated either on their own roots or on compatible root stocks of a different kind. This makes it easy to assess the effects of the environment if cuttings from the same plant, for example, are raised in pots and subjected to different soil and climatic conditions so allowing the effects of these conditions to be measured without having to worry about the part played by genetic variation.

On the other hand, if one wishes to compare the performance of different seedlings in terms of their genotype they must be raised under identical conditions as otherwise it would be very difficult to disentangle the effects of genetic and environmental factors. This has relevance to Breedplan and points to the need to see that all animals are raised on an even playing field wherever possible or else that suitable adjustments are made.

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