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 a positive correlation between the traits selected than the result will be desirable and if there is a 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. The efficiency of this method is low.
3. It takes a very long period to achiever desirable efficiency. In the meantime, the breeder may change his goal.
4. If there is an undesirable correlation between traits that will also hinder 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 a 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 to be selected.
• The failure to meet the minimum standard 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 the Tandem method because simultaneous selection is made for more than one trait.
2. Independent culling levels are easy to perform.
3. It allows the culling of animals earlier, which are inferior in early expressed traits.

Demerits

1. In this method, there is the 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 number of animals to be saved for breeding. Therefore, this method reduces the selection intensity with an increase in several 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 the selection of animals for show purposes where the animals are selected for type, color, and body confirmation traits ignoring their 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 included the in selection.
• In total score or selection index meth, od 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, the selection index is a total score that includes all the advantages and disadvantages of an animal.
• The animals with the highest score/index are selected for breeding.

Merits

1. The 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 the index method increases with the number of traits. Thus it requires less time to bring about an overall improvement.