There are genetic correlations between many of the production characters in the Merino. If the correlation is positive, then selection for an increase in the first character, results in an increase in the second character, in the progeny. Similarly, if the correlation is negative, selection for an increase in the first character will result in a decrease in the second character in the progeny. Their significance in selection programmes Such correlations can result in undesirable changes, for example, there is a medium positive genetic correlation between clean fleece weight and fibre diameter. It is very important, therefore, that any selection program with a breeding objective to increase clean fleece weight does not ignore fibre diameter.
Measurement is needed to control fibre diameter.
The breeder may wish to keep fibre diameter at its present level or to decrease it. Whatever the choice, Rampower can provide an appropriate index which will allow a breeder to achieve the particular breeding objective. Many of the relationships, however, can produce beneficial changes in the progeny. For example, a positive genetic correlation between clean fleece weight and staple length, means that selection for clean fleece weight results not only in increased fleece weight in the progeny, but also increased staple length. Similarly, the negative correlation between wrinkle score and clean fleece weight means that selection of plainer sheep, results in increases in clean fleece weight in the next generation.