Multiple trait selection- Selection index

1. MULTIPLE TRAIT SELECTION
PRESENTED BY,
S.DIVYA
PhD scholar in Genetics and Plant Breeding
TAMIL NADU AGRICULTURAL UNIVERSITY,
Coimbatore- 641003

2. Multiple trait selection
A selection program which usually focus on several
traits of economic importance is known as multiple
traits selection.

3. Multiple trait selection
• Genetic, environmental & Phenotypic correlations are
required for efficient multiple trait selection
• Phenotypic correlation-two traits such as height and
weight can be correlated
• Genetic correlation- the genetic values for 2 traits are
correlated
• Environmental correlation- the environmental effects on
the 2 traits are correlated

4. Multiple trait selection
• The definition of a correlation is the covariance
between 2 traits divided by the square root of the
product of the variances of the 2 traits
Phenotypic correlation = 2
2
2
1
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5. • Selection objective
• all traits that contribute to economic efficiency
• Selection criterion
• all traits that are evaluated for improvement of the
selection objective
• Not necessarily the same traits

6. Methods of multiple trait selection
• Tandem
• Independent culling levels
• Selection index

7. Tandem selection
• The tandem method of selection as described by
Hazel and Lush (1942) involves selection for one
trait at a time.
• This is followed by selection for a second trait,
third trait, etc., until the desired level of
improvement is reached.
• The long generation interval of most forest tree
species would appear to preclude use of the
tandem method by the tree breeder.
• However, there are circumstances in which the use
of this method is justified.

8. • Such situations exist in cases where a single
characteristic limits the economic usefulness of a
species.
• An example of such a condition occurs in breeding
for disease resistance where the disease is a
completely limiting factor in the management of a
species.
• Gingham et al. (1960) discuss such a situation in
breeding for resistance to Cronartium ribicola &
Fisher in Pinus monticola Dougl.

9. • Efficiency of tandem selection depends a great deal
upon the genetic correlation between the traits
selected for.
• If the genetic correlation is positive and desirable,
improvement in one trait by selection would
automatically result in improvement in the other
trait.
• When the two traits are negatively correlated,
improvement in one trait is nullified or neutralized
by the regression in the other

10. Tandem selection -Difficulties
 Genetic correlations must be known
 Correlations and heritabilities must remain the
same over several generations of intense selection
for one trait
 Economic values are linear
 Economic value does not change over time
 Not very effective
 Especially bad if adverse correlations among traits

11. Independent Culling Levels
• Selection is made simultaneously for all the characters but,
independently, rejecting all individuals that fail to meet the
minimum standard for any one trait.
• Individuals falling below this level for a given trait will be
rejected regardless of their superiority in other traits.
• It is never more efficient than the selection index method.
• But, in cases where, the traits under consideration manifest at
different ages, it offers the practical advantage of disposing a
proportion of inferior individuals earlier.

12. Independent Culling Levels-
Advantage
• This method is more efficient than tandem method
and has an important advantage over the latter in
that, selection is practised for more than one trait
at a time.
• In some cases the method allows selection for
given traits before the organism under
consideration has matured.
• For example, disease resistance generally can be
evaluated fairly early in the life of the tree,
permitting selection for this trait long before other
traits can be evaluated.

13.  Many of the present tree breeding programmes select
plus trees by scoring systems (Andersson, 1965; Cech,
1959; Stern and Hattemer, 1964), but selection for
certain traits such as resistance to disease and bole
straightness is based on independent culling levels.
 can cull sequentially
Selection will occur in stages corresponding to level of
maturity

14. Independent Culling Levels
Disadvantage
• If traits are correlated, calculating expected response
is difficult .

15. Selection index
• The method of total score (Hazel and Lush, 1942) or selection index (Hazel, 1943) has
been shown never to be inferior to the method of independent culling levels.
• The method of the selection index was initially applied to selection in plants by Smith
(1936).
• He used Fisher's concept of discriminant functions to develop a selection guide for
determining plant lines which had the greatest genotypic value.
• Numerous selection indices have been developed for crop plants (see Robinson et al.,
1951; Johnson et al., 1955; and Brim et al., 1959).
• More recently, selection indices have been developed for forest trees by van Buijtenen
and van Horn (1960) and Illy (1966).

16. Selection index
• Selection is made for all traits simultaneously by using
some kind of a total score or index of the net merit of
an individual, constructed by combining together the
scores for component characters.
• The individuals with highest score are kept for
breeding purposes.
• Since the traits to be considered in selection may not
be equally important economically, some kind of
weighing is required.

17. Selection index
• Equation that combines all traits of importance
• H = v1X1 + v2X2 + ….. VnXn
• Where vi are selection index and xi are the phenotypes of an individual
Factors in calculation
• economic importance
• heritability
• standard deviation
• genetic correlations
• phenotypic correlations

18. Selection index
Disdvantage
• strength in one trait can make
up for weakness in another
Advantage
• should measure all traits on all
selection candidates

19. Selection index- Advantage
 Maximizes the correlation between the true
additive genetic merit and its predicted value
(accuracy of evaluation)
 Minimizes the average squared prediction error
(minimizes prediction error)
 Genetic gain is faster with this method than with
any other
 Procedure is unbiased (average of prediction
error for all animals is zero)

20. • Selection index method is more efficient than
tandem and independent culling level methods,
because it results in more genetic improvement for
the time and effort expended in its use.

22. REFERENCES
• 1. B.r,rnn, R. J. 1956. Predicted variance of response
ro selection. Ph.D. Thesis, University of Minnesota,
St. Paul, Alinn.
• 2. Bexr,n, R. J., BnNlnr.o,r.v, V. AtI. and KeurueNN,
M. L. 1968. Inheritance of and interrelationships
among yield and several quality traits in common
wheat. Crop Sci. B, 725-728.
• 3. Bocren, W. A. 1968. A'Ianual of procedures in
quantitative genetics. Washington State Universiry
Piess, Pullman, Washington.
• 4. BnIr,r, C. A. 1966. A modified pedigree method of
selection in soybeans. Crop Sci. 6, 220.

23. THANK YOU…..