2. TRIPLE TEST CROSS
ANALYSIS
CROSSING OF RANDOMLY SELECTED F2 PLANTS WITH BOTH THE PARENTS
(P1 AND P2) INVOLVED IN THE CROSS, AND ALSO WITH THEIR F1 HYBRID IS REFERRED
TO AS TRIPLE TEST CROSS AND ANALYSIS OF A SET OF SUCH CROSSES IS CALLED TRIPLE
TEST CROSS ANALYSIS.
CONCEPT WAS DEVELOPED BY KEARSEY AND JINKS IN 1968.
EXTENSION TO NORTH CAROLINA DESIGN 3 OF BIPARENTAL CROSS.
3. Main Features
Analysis involves both first order and second order statistics.
Provides reliable information about the presence or absence of epistatis, in addition to
estimates of additive and dominance variances.
Each randomly selected F2 plant is crossed with inbred parents of the original cross and
also with their F1.
Requires 4 crop seasons for complete study. Three crop seasons are required for
developing material and fourth season for evaluation of material.
Results are reliable and have high degree of precision.
This technique is applicable for both self and cross pollinated crops
Not in common use in plant breeding and genetics unlike diallel, partial diallel and line x
tester analysis.
4. Main steps
Selection of parents- inbred lines, strains and cultivars. Parents should have contrasting
characters.
Selected parents are crossed in first yr to obtain F1
F1 raised and self pollinated in second yr to obtain F2.
From F2 population some random selected plants designated as male are backcrossed
with parents(p1 and P2) and F1 which are used as females.
In fourth season back crossed populations along with parents and F1 are evaluated in
replicated field trial and observations are recorded on various polygenic traits.
Biometrical analysis is done according to singh and Chaudhary, 1985.
5. Advantages
Provides reliable information about the presence or absence of epistasis,
in addition to estimates of additive and dominance variances
It provides independent estimation of additive genetic variance and
dominance variance.
6. limitations
This technique takes more time for evaluation of parents than diallel
cross analysis. 4 crop seasons required for developing breeding
material and fourth season for evaluation of material.
Choice of inbred lines with contrasting characters is difficult.
7. Test of epistasis
TTC provides information about the presence or absence of non allelic
interactions.
Following relationship provides for presence or absence of epistasis:
L1 + L2 – 2L3 = 0
Where L1, L2 and L3 are the mean values of progenies derived from
mating of F2 with P1, P2 and F1, respectively.
8. Inference
If value is 0, it indicates absence of epistasis
If value is greater than 0, it indicates presence of epistasis.
Significance of epistasis can be tested either by t test as in scaling test
or by F test.
If epistasis is absent estimation of D and H components can be done
without the transformation of data, while in the presence of epistasis
transformation is essential.
9. Modification
When the population under investigation Consists of highly inbred lines the full triple
test-Cross of Kearsey and Jinks (1968) supplemented by the selfed progenies of the
population allows unambiguous and independent tests for epistasis and the adequacy of
the pure-breeding testers, L1 and L2. This can also be achieved by supplementing the
simplified triple test-cross of Jinks, Perkins and Breese (1969) with the selfed progenies of
the L1i and L2i families. If the L1 and L2 testers prove to be inadequate due to the
presence of common loci, modifications of the analyses are proposed which Correct the
resulting biases in the genetical components of variation
Testers L1, L2 and their hybrid (L3) are crossed with a number of unrelated strains rather
than crossing with F2 individuals of the cross.
This modified scheme is similar to TTC, has similar statistical analysis and provides
comparable results.
