1 gpb 621 quantitative genetics introduction

1. Principles of Quantitative Genetics -Introduction
GPB 621 –PRINCIPLES OF QUANTITATIVE GENETICS
Class -1
Dr. K. SARAVANAN
Professor
Department of Genetics and Plant Breeding
Faculty of Agriculture
AnnamalaiUniversity

2. Dr.K. Saravanan, GPB, AU
•Statistics
•Biometrics
•Biometrical Genetics / Quantitative Genetics
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3. Dr.K. Saravanan, GPB, AU
History of Quantitative Genetics
•Mendel laid the foundation of the genetics.
•Mendel observed seven clear cut visible traits in garden pea (Pisumsativum) and
postulated laws of inheritance of characters.
•Themathematicalfoundationsforthestudyofquantitativevariation
werefirstlaidbyGalton(1989).
•Hestudiedthephysicalandmentalcharacteristicsofhumanbeings.Heobserved
thattallerindividuals,producedtallerchildrenonanaverage.Tomeasurethedegree
towhichsuchcharacteristicswereinherited,newbiometicaltechniquessuchas
correlationandregressionweredevelopedbyGaltonandhisstudents.
•In 1900 Mendel’s work was rediscovered.
•Differentviewsformedthebasisforthetwomaingroupsamonggeneticists,namely
“Mendelians”whoproposedthatheritablecharacterswerequalitativeand
discontinuous(discrete)indistributionand“biometricians”whobelievedthatthe
heritablevariationwasbasicallyquantitativeandcontinuousindistribution.
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4. Dr.K. Saravanan, GPB, AU
•Yule(1906)–
•considerbothgroupsandgivesuggestedthatthereneedbenoconflict
betweenparticulateinheritanceandcontinuousinheritanceifmanygenes
havingsmallandsimilareffectswerepostulated.
•Johannsen(1909)
•Indemonstratingtheoccurrenceofquantitativegeneticvariation,statedthat
bothheritableandnonheritablefactorswereresponsibleforvariations
observedintheseedweightofbeans(Phaseolusvulgaris).
•P=G+E
•Nilson-Ehle(1909)–Multiplefactorhypothesiswasproposed.
•Devanport(1913)
•AnalysedtheskincolourinheritanceintheprogenyofNegro-Whitemating
andconcludedthatthehypothesisofmultiplefactorsexplainstheinheritance
ofskincolourinMulattoes.
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5. Dr.K. Saravanan, GPB, AU
•East (1916)
•Conclusiveevidenceforthehypothesisthatseveralgeneswithsmall,similarand
additiveeffectsgoverntheinheritanceofquantitativecharacterswasprovidedby
E.M.Eastin1916.Eastbeganhisstudieswithtwotruebreedingvarietiesoftobacco
(Nicotianalongiflora)thatdifferedinrespectofflowerlength.
•Fisher (1918)
•ShowedhowthebiometricalfindingscouldbeinterpretedintermsofMendel’s
factors.
•Heshowedhowstatisticallytheeffectofenvironmentcanbepartitionedform
geneticeffects.
•Heprovidedtheinitialframeofbiometricsforthestudyofquantitativegenetics.
•Healsopartitionedthegeneticvariancetoadditive,dominanceandepistatic
components.
•InsobringingtogethertheGaltonapproachandtheMendelianbasis,Fisherlaidthe
foundationforquantitativegenetics.
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6. Dr.K. Saravanan, GPB, AU
MendelianVsPolygenic Traits
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MendelianGenetics Biometrical Genetics
1.GovernedbyOligogenes GovernedbyPolygenes
2.Thevariationisdiscontinuous Thevariationiscontinuous
3.Theindividualscanbegroupedintodistinct
classes
Theindividualscannotbegroupedintodistinct
classes
4.Theexpressionofthecharacterisleast
influencedbytheenvironment
Theexpressionofthecharacterishighly
influencedbyenvironment
5.Theinheritancecanbestudiedbygrouping
theindividualsintodistinctMendelian
ratios.(Basedonfrequenciesandratios).
Sincetheindividualscannotbegroupedinto
distinctratios,theinheritancecanbestudiedby
statisticalquantitieslikemean,varianceandco-
varieance.

7. Dr.K. Saravanan, GPB, AU
Features of Polygenes
1.Thevariationduetopolygenesiscontinuousbetweentwoextremes
2.QuantitativevariationisgovernedbySeveralGenes
3.Theeffectofeachgeneissmallorminorbuttheeffectiscumulative
4.Classificationofquantitativecharactersintodiscretegroupsisnot
possible
5.Quantitativecharactersareinfluencedbyenvironment
6.Theeffectduetopolygenesisqualitativei.e.,measurable
7.Quantitativetraitsexhibittransgressivesegregation
8.Polygenesarestableintheirinheritance
9.Polygenesexhibitlowheritability
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8. Dr.K. Saravanan, GPB, AU
Types of Statistics : (Mather and Jinks, 1971)
•First degree
•Second degree
•Third degree
(The major part of biometrical analysis is based on first and second degree statistics.)
First degree:
•It is also known as first order statistics.
•It includes mean, which is used for the measurement of all types of parameters.
•The calculation of first order statistics is simple and reliable.
•It is used to study of
•Generation mean
•Heterosis
•Inbreeding depression,
•Metroglyphanalysis
•Stability analysis
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9. Dr.K. Saravanan, GPB, AU
Second degree:
•It is also known as second order statistics.
•It includes estimates of variance and co variances
•The calculation of second order statistics is more difficult than first order
statistics.
•It is used to estimation of
•Correlation
•Path analysis
•Discriminant function
•D
2
Statistics
•Heritability
•Genetic advance
•Components of variance in diallele, Partial diallele, L x T, Triple test cross and
biparentalcrosses.
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10. Dr.K. Saravanan, GPB, AU
Third degree:
•It is also known as third order statistics or higher order statistics.
•It includes complex interaction like kurtosis and skewness
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11. Dr.K. Saravanan, GPB, AU
•The various statistical procedures which are employed in the
biometrical genetics are called biometrical techniques.
•In plant breeding
1.Assessment of variability
2.Selection of elite genotypes
3.Choice of suitable parents and breeding procedures
4.Assessment of stability of genotypes.
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BIOMETRICAL TECHNIQUES AND STATISTICAL PARAMETERS IN PLANT BREEDING

12. Dr.K. Saravanan, GPB, AU
1.Assessment of variability
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Biometrical techniques Genetic information obtained about
1.Simple measures of variability viz., range, SD, CV,
Variance etc.,
Phenotypic variability
2.Componentsof genetic variance Genetic variability
3.D
2
statistics Genetic diversity
4.Meteroglyphanalysis Variability and diversity
2. Selection of elite genotypes
Biometrical techniques Genetic information obtained about
1.Correlation analysis Character association
2.Path analysis Cause and effects
3.Discriminant function Selection criteria

13. Dr.K. Saravanan, GPB, AU
3. Choice of suitable parents and breeding procedures
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Biometrical techniques Genetic information obtained about
1.Diallelcross analysis gca, scavariance and effects and D & H
2.Partial diallelanalysis All above estimates except scaeffects
3.Lx T analysis gca, scavariance and effects and D & H
4.BiparentalMating Additive and dominance variance
5.Triple Test cross Analysis D, H and presence or absence of epistasis
6.Generation Mean Analysis Additive,dominance and epistaticvariance
4. Assessment of stability of genotypes
Biometrical techniques Genetic information obtained about
1.Various stability models Phenotypic stability

14. Dr.K. Saravanan, GPB, AU
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15. Dr.K. Saravanan, GPB, AU
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16. Dr.K. Saravanan, GPB, AU
Multiple factor inheritance :
Problem 1.
Assumethattwopairsofgeneswithtwoalleleseachdetermineplantheight
additivelyinapopulation.ThehomozygoesAABBandaabbhave50cmand30
cmheightrespectively.
a). What is the height of F
1in a cross between these two homozygous plants.
b). After F
1x F
1cross, which genotypes in F
2will show a height of 40 cm.
c). What will be the F
2frequency of these 40 cm plants.
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17. Dr.K. Saravanan, GPB, AU
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18. Dr.K. Saravanan, GPB, AU
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19. Dr.K. Saravanan, GPB, AU
Problem 2.
Threeindependentlysegregatinggeneseachwith2allelesdetermineheightina
particularplant.Thepresenceofeachcontributingalleleadds2cmtohebase
heightof2cm.
a). Give the height expected in F
1progeny of a cross between dominant homozygote and
recessive homozygote.
b). Give the distribution of height expected in a F
1x F
1cross.
c). What proportion of this F
2progeny would have heights equal to the parental stocks.
d). What proportion of F
2would breed true for the height shown by F
1.
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20. Dr.K. Saravanan, GPB, AU
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21. Thank q
Dr.K. Saravanan, GPB, AU