Family selection involves selecting or rejecting entire families based on the average performance of family members. It is commonly used in species like swine and poultry with large family sizes. Family selection can provide information about traits that are only expressed in one sex or late in life. While it utilizes information from relatives, the accuracy of selection depends on factors like heritability and environmental correlations between relatives. Pedigree selection uses performance records of ancestors to estimate an individual's genetic merit, but distant ancestors provide less information and there are limitations to relying solely on pedigree.

1. Topic: Basis of Selection
Family Selection
Dr S.Shanaz

2. BASIS OF SELECTION - FAMILY SELECTION
• Family, in Animal breeding, includes full-sib and half-sib families
( half-sibs : relationship coefficient of 0.25 and full-sibs 0.5)
• These family members are collaterally related not directly related. They are
neither ancestors nor descendants.
• Family selection: Individuals records are included in the family averages
• sib selection: Individuals’ records are not included in the average,
 When selection is carried out for market weight ,the weights of all males
and females in the family are considered in calculation of family average
(family selection). But when selection is carried out for fertility traits and
milk yield, the performance of males cannot be included but they are
selected on the basis of sibs’ average (sib selection).
• Family selection can be represented as a part of pedigree selection.
• The families are ranked and based on this, the entire family is selected or rejected

3. • Family/sib selection is used more frequently in swine and poultry where
the number of progenies produced by females is high.
• The information from family/sib is combined with individuals
information in the form of index and selection is based on the index.
• Collateral relatives are those not directly related to an individual as
ancestors or progeny
• These are neither direct ancestors nor direct descendants of an
individual. may be individual’s brothers, sisters, cousins, uncles, aunts,
nieces, nephews, etc.
• The more closely they are related to the individual in question, the more
valuable information they provide for selection purposes
• If information on collateral relatives is complete, it gives an idea of kinds
of genes and combination of genes the individual is likely to possess

4. • Useful in selecting traits that can be measured only after the
sacrifice of the individual e.g. carcass traits
• Useful in selecting dairy bulls, since milk production can be
measured only in cows though bull possesses and transmits genes
for milk production to his progeny.
• It is also used in selection of poultry for egg and meat production
and also for all or none traits such as mortality, disease resistance
and fertility
• Selection on the basis of sib tests (Half sibs or Full sibs) means that
an individual is kept for breeding or is rejected on the basis of the
phenotype of its brothers and sisters
 They may be maternal half sibs or paternal half sibs or full sibs.
USES OF FAMILY SELECTION

5. • The accuracy of selection on the basis of collateral relatives depends upon
heritability, relationship R of the sibs and individual being selected, number of sibs
used to determine the sib average, degree of correlation (t) between the
phenotypes of sibs.
• Accuracy of selection = Rh  n / 1 + (n-1) t
If environmental correlation among the phenotypes of the sibs are zero, then
t = Rh2
• Accuracy of selection increases as the records on a large number of half sibs are
considered and as heritability increases. The accuracy of selection never exceeds
0.5, regardless of number of half-sibs tested and heritability of that trait
• Nearly 30 half sibs are required to give the same accuracy as information on the
individual’s own record when heritability is as low as 0.10 and 100 or more when
heritability is higher than 0.10.
• However in instances where information cannot be obtained from the individual,
such as sex limited traits can be used effectively in selection
PROBABLE BREEDING VALUE

6. • Full sibs may be used in selection, but they have a similar maternal
environment from conception to weaning , lowers the accuracy of their use
for such a trait
• Selection on the basis of individuality is relatively more accurate than
selection on the basis of full sib records when the trait is highly heritable
• When heritability is low, and records on six or more full sibs are available
then selection on the basis of full sibs is more accurate
• The combination of records on the individual and its sibs for selection is
more advantageous than records on the individual’s own performance
when R and t are greatly different
• It is more useful when difference between families are mainly due to
environment because different families have been treated differently

7. Families can be broadly classified into three types:
Sire families: These are progeny of one sire
 Out of different dams – born in the same year (contemporaries)
 Out of different dams – born over a number of years
Dam families
 By different sire – born in the same year i.e. by super ovulation before
artificial insemination with mixed semen from number of sires and
identification of sires by blood typing
 By different sires – born over a number of years
Sire and dam families:
These are progeny by one sire out of one dam
• Family selection is more effective when the genetic relationship
between members of the same family is large, and the phenotypic
relationship between members is small
• When heritability is low, the use of family data is most valuable as it
reduces the chances of making wrong decisions

8. Indications of Family Selection
• For sex-limited traits
• For carcass traits and
• For traits of low heritability
Limitations
• If selection intensity is more, then there may be an increase
in inbreeding
• Increase in cost and space in raising larger population
Precautions
• Number of progeny in each family should be large and
• There should not be common environment between sibs

9. PEDIGREE SELECTION
• Pedigree is a record of an individual’s ancestors related to it through its
parents
• Selection based on information of the ancestors of individuals that are
related to it
• Performance records from ancestors can provide useful information about
the potential genetic worth or the breeding value of the individuals
An estimate of calf’s potential milk yield could be assessed based on milk yield
of its mother until the calf is grown up and can be milked
• Much attention is to be paid to pedigree when no adequate information on
the merit of the individual is available
• Parents never provide as much information about the breeding value of an
individual than individual’s performance itself would provide. Unless the
performance of ancestor is known, selection based on pedigree is
meaningless

10.  The relationship between the individual and ancestor is very
important
 Distant ancestors of an individual provide even less genetic
information about the individual’s breeding value especially for
production traits
Pedigree can be classified into two: Direct and collateral
• Collateral means those descended from same ancestors. Selecting a cow
based on the performance of its great grand parent is as good as random
selection because the relationship is (1/2)3 = 1/8 i.e. only 1/8th of the
superiority can be expected in the progenies
• It s not useful beyond three generations due to halving process of the
chromosomes in each generation
• Pedigree selection can be made more useful by giving all information
good and bad about ancestors, including the collateral relatives.

11. • Useful in initial selection for traits that are expressed in one sex
only , selections can be made early and inexpensively
• For high heritability traits little is gained from considering ancestors
and most progress could be made by evaluating the individual itself
e.g. horned condition
• The selection based on pedigree is only useful than of individual
selection only when heritability is moderate or low. The average
relationship between one parent and offspring is 0.5
• Pedigree information on both the parents should be available to give
more reliable estimate of the genotype of the offspring
• When the pedigree data provides information on the phenotypic and
genotypic merit of the ancestors then it is called performance
pedigrees

12. • Degree of relationship
Ancestors more closely related to the individual should receive most
emphasis in pedigree cosideration appraisal
(Parent – 0.5, grand parent – 0.25 and great grand parent – 0.125)
• Degree of heritability
When heritability of the trait is low, the more remote ancestors
should receive relatively more emphasis, but when it is high they
provide almost no new information
• Environment correlation
Pedigree selection is accurate when heritability is high. The
correlation between pedigree information and individual’s breeding
value approaches the theoretical 0.71 as heritability approaches 1.0.
Dangers of pedigree selection
 Undue emphasis on remote relatives
 Unwarranted favoritism towards the progeny of favoured individual

13. • Pedigrees are cheap to use
• Used to select traits not expressed early in life or still immature and
when their production records are not available .g. cancer, tumour,
longevity etc
• Used to select traits expressed in only one sex (sex limited)
• Useful when selection based on individuality is not accurate
• When production performances of the individuals are not available
• For making preliminary selection of sires in progeny testing
• When the characters are expressed late in life
• For traits with low heritability pedigree information can be combined
with individual’s records
Advantages

14. Disadvantage
A disadvantage of the use of the pedigree in selection against a
recessive gene is that there are often unintentional and
unknown mistakes in pedigrees that may result in condemnation
of the entire family from breeding even when actually it may be
free of such a defect

15. LIMITATIONS OF PEDIGREE SELECTION
• Since phenotype is not the true indicator of genotype due to
complications by dominance, epistasis and environment prediction of
genotype is difficult
• When the phenotypic value of an individual is known not much is
gained by the use of pedigree
• Pedigree contains ancestors that are selected and hence contains
only selected information to show them in a favourable light and tells
very little about the collateral relatives
• The pedigree records are made in different environment and hence
the accuracy of the ancestry may not be reliable
Unwanted favouritism towards the progeny of the favoured individual.