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Selection Index and its Precision | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Introduction

The concept of employing a selection index or total score in breeding programs has its roots in the work of Birth and Harel. This approach involves assigning index values to individuals, aiming to achieve the closest correlation possible with the composite breeding values of each individual. The utilization of an index is crucial for the efficient selection of multiple traits.

Importance of Selection Index

  • Economic Importance: Not all traits considered in selection hold equal economic significance. Differential weighting is necessary, aligning with the economic return expected from improving each trait. This tailored approach ensures optimization in overall economic value.
  • Variability in Heritability: Traits exhibit varying heritability levels, implying that the same intensity of selection may not yield proportional improvements for all traits.
  • Interrelationships among Traits: Phenotypic and genetic interrelationships among traits necessitate consideration. Emphasizing one trait may impact others, requiring a comprehensive approach to selection.

Information Required for Developing a Selection Index

  • Relative Economic Importance: Knowledge about the relative economic importance of each trait guides the definition of selection goals. The aim is to improve the overall enterprise, with traits weighted according to their economic significance.
  • Heritability and Variance: Information on the heritability and genetic variance for each trait, as well as the phenotypic variance, is crucial for understanding the potential for genetic improvement.
  • Covariances: Understanding the phenotypic and genetic covariances among traits, often expressed through correlations, is essential for accurate selection decisions.

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What is the purpose of employing a selection index in breeding programs?
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Optimal Selection Procedure

  • The most effective selection procedure involves utilizing all available information to estimate each individual's breeding value, creating an index of merit. This comprehensive approach ensures a holistic evaluation of multiple traits, aligning with the overall breeding goals of the enterprise.
  • In the realm of animal and plant breeding, effective selection strategies demand a wealth of information sourced from various relatives, encompassing not only individuals but also parents, full siblings, half-siblings, and more. When traits are sex-limited, data on unmeasurable individuals must be derived from different types of relatives. The ultimate goal is to amalgamate this diverse information into a unified index, forming the basis for intelligent selection decisions.

Multiple Trait Selection

  • Selection for the enhancement of economic value in animals or plants is a complex task that involves considering several traits simultaneously, rather than focusing on a single trait. This approach, known as multiple trait selection, recognizes that economic value hinges on the interplay of various characteristics. 
  • For instance, the profitability of a pig herd is intricately tied to factors such as fertility, mothering ability, growth rate, food utilization efficiency, and carcass qualities.

Optimizing Economic Value

  • To achieve the swiftest enhancement of economic value, the most effective method involves applying selection concurrently to all relevant traits. Each trait receives appropriate weighting, factoring in its relative economic importance, heritability, and the genetic and phenotypic correlations between traits.
  • The integration of these component traits into a cohesive score or index facilitates selection as if it were a single character. This approach ensures the most expeditious improvement of economic value.

Question for Selection Index and its Precision
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What is the purpose of utilizing a comprehensive selection procedure that estimates each individual's breeding value and creates an index of merit?
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Precision or Efficiency of an Index

The degree of correlation between index values and breeding values serves as a metric for the efficiency of an index. Essentially, a higher correlation indicates a more effective index in predicting breeding values. The construction of the index is optimized to maximize its utility in leveraging available information. Comparisons among various indices, formed with different measurements, can be made by assessing their correlations. This analysis helps determine the inclusion or exclusion of specific traits in the index, enhancing its overall effectiveness. 

The efficiency (rLa) is computed as follows:
The index of the individual is I = b1, P1 . b2 P2 + b3 P3 +...
The equations for variances and covariances of the breeding value are

Selection Index and its Precision | Animal Husbandry & Veterinary Science Optional for UPSC

First, we need to know the variance of index values. Equation (1) can be seen as

Selection Index and its Precision | Animal Husbandry & Veterinary Science Optional for UPSC

where variances and covariances are written in the notation of equation (2) This expression can be put into a form that is easier to calculate Rearranging the terms gives

Selection Index and its Precision | Animal Husbandry & Veterinary Science Optional for UPSC

Substituting for the term in brackets from equation (2) leads to
Selection Index and its Precision | Animal Husbandry & Veterinary Science Optional for UPSC

Next, we need to know the covariance of index values with breeding values. This is Selection Index and its Precision | Animal Husbandry & Veterinary Science Optional for UPSC for the following risen. 

The efficiency of an index is gauged by the correlation between index values and breeding values, with a higher correlation indicating superior predictive capabilities. The scaling of an index ensures that one unit of the index corresponds to one unit of the predicted breeding value, maintaining a correlation of unity (r = 1). This correlation is essentially the multiple correlation, showcasing the proportion of additive variance accounted for by the measurements integrated into the index. Conversely, (1-r2) signifies the unaccounted fraction of additive variance, leaving room for further improvement by incorporating additional measurements.

Selection in Retrospect

Conducting selection experiments with livestock is a resource-intensive process, requiring several years for conclusive outcomes. However, recent evidence underscores the efficacy of selection in altering animal populations. Notable experiments with Drosophila and laboratory mammals, including rats, demonstrate the impact of selection on quantitative traits.

Selection in Plants:

  • The landmark example of selection potential is the Illinois selection experiment for high and low corn oil content. 
  • Starting with an initial oil content of 4.68 percent, the high line increased to 16.64 percent, while the low line decreased by less than one percent, showcasing the tangible outcomes of selection.

Selection of Laboratory Mammals:

  • Castle's pioneering work on quantitative traits in rats, particularly selection for hooded patterns, exemplifies the outcomes of selection in laboratory mammals. 
  • Long-term responses to selection for body size in mice have been extensively reported, demonstrating significant genetic changes attributed to selection.

Selection Plateaux

  • Experiments involving selection for highly heritable quantitative traits in laboratory animals, such as mice, rats, Drosophila, and Tribolium castaneum, have shown rapid responses over 10 to 30 generations. 
  • However, these populations often exhibit plateaus, indicating a point beyond which further improvement slows or ceases. 
  • The concept of plateaus is explored in the context of farm animals, where the effectiveness of selection for economically important traits is still under investigation.

Question for Selection Index and its Precision
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What is the measure of efficiency for an index?
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The document Selection Index and its Precision | Animal Husbandry & Veterinary Science Optional for UPSC is a part of the UPSC Course Animal Husbandry & Veterinary Science Optional for UPSC.
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FAQs on Selection Index and its Precision - Animal Husbandry & Veterinary Science Optional for UPSC

1. What is the selection index in the context of the UPSC exam?
The selection index in the context of the UPSC exam refers to a measure used to rank candidates based on their performance in the exam. It is a composite score derived from various factors such as the candidate's scores in different papers, interview performance, and other criteria set by the UPSC.
2. Why is the selection index important in the UPSC exam?
The selection index is important in the UPSC exam as it helps in determining the final merit list of candidates. It provides a fair and standardized method of evaluating candidates' performance across different papers and stages of the exam. The selection index ensures that candidates with the highest overall scores are selected for the desired positions.
3. How can the selection procedure be optimized for the UPSC exam?
The selection procedure for the UPSC exam can be optimized by ensuring the inclusion of multiple stages, such as the preliminary exam, main exam, and interview. This multi-stage approach allows for a comprehensive evaluation of a candidate's knowledge, skills, and abilities. Additionally, the selection criteria and weightage assigned to different components of the exam can be regularly reviewed and updated to ensure fairness and objectivity.
4. What is the significance of precision or efficiency in the selection index?
Precision or efficiency in the selection index refers to the ability of the index to accurately rank candidates based on their performance. A precise selection index ensures that candidates with higher scores are ranked higher, while an efficient index minimizes the likelihood of errors or misjudgments in the ranking process. A high precision and efficiency in the selection index enhance the credibility and reliability of the entire selection process.
5. How does the selection index factor into retrospective analysis of the UPSC exam?
The selection index plays a crucial role in retrospective analysis of the UPSC exam. By analyzing the selection index of successful candidates from previous years, trends and patterns can be identified. This analysis helps in understanding the factors that contribute to success in the exam, enabling candidates to focus their preparation on the areas that carry more weightage in the selection index. Additionally, retrospective analysis allows for the evaluation of the effectiveness and fairness of the selection process over time.
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