Methods of Selection

a) Tandem Method:

• Selection is practiced for only one trait at a time until improvement has been made in the trait.
• Selection efforts for this trait are then relaxed and efforts are directed towards the improvement of a second, then a third and so on.
• The efficiency of this method depends on the genetic correlation between traits.
• If there is positive correlation between traits selected than the result will be desirable and if there is negative correlation the effect will be undesirable.

Merits

1. It is simple to practice
2. The intensity of selection is more
3. If there is a desirable genetic correlation with other traits, it produces progress in the related traits.

Demerits

1. Only one character is considered at a time.
2. Efficiency of this method is low
3. It takes very long period of time to achiever desirable efficiency. In the mean time the breeder may change his goal.
4. If there is undesirable correlation between traits that will also hinder the progress, i.e. genetic improvement obtained in previous generations will be lost.

b) independent culling Method:

• In this method, selection may be practiced for two or more traits at a time or at different times in the lifetime of an individual.
• In this method, for each trait a minimum standard is set so that each animal must meet those standards in order to be selected.
• The failure to meet the minimum stand for any one trait makes the animal to be rejected.
• The effectiveness of this method depends on the level kept for each of the traits.

Merits

1. This method is superior to Tandem method because simultaneous selection is made for more than one trait.
2. Independent culling levels are easy to perform.
3. It allows culling animals earlier, which are inferior in early expressed traits.

Demerits

1. In this method there is possibility of culling genetically superior animals for some traits if they are less than the culling levels for any one for the traits whereas mediocre animals those just meeting the minimum standards are likely to be selected.
2. The proportion selected for each trait will depend on the total animals to be saved for breeding. Therefore, this method reduces the selection intensity with increase in number of traits to be selected.
3. If genetic correlations among traits are in the undesirable direction, it will further reduce the efficiency. Generally, this method has been used in selection of animals for show purposes where the animals are selected for type, color and body confirmation traits ignoring its performance for economic traits.

c) Selection Index or Total Score Method:

• Index Selection is a method of artificial selection in which several useful traits are selected
• In this method the animal is cored for its merit in each of the traits include in selection.
• In total score or selection index method culling levels are flexible.
• An index is a single numerical value, which is the total of scores given for each trait considered in the selection.
• Each trait is weighted by a score and the individual scores are summed to a total score/index value for each animal which is the selection criterion.
• By this method, superiority in some traits can be made up by mediocrity in others. Thus, selection index is a total score that includes all the advantages and disadvantages of an animal.
• The animals with highest score/index are selected for breeding.

Merits

1. Most efficient method of selection among the three methods.
2. It allows the individuals, which are superior in some traits to be selected regardless of their deficiency in other traits.
3. All the characters are given proper weightage for optimum selection.
4. The advantage of index method increases with the number of traits. Thus it requires less time to bring about an overall improvement.