PowerPoint Presentation

APresentationON Mapping Population & its application in Agricultural Biotechnology

By:ANIRUDH KUMARId. NO -1632 (B.Tech. Biotech.)College of BiotechnologySardar Vallabhbhai Patel University of Agriculture & Technology, Meerut - 250110

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Introduction

A populationusedfor genemappingiscommonly calledamappingpopulation.

Mappingpopulations are usually obtained from controlled crosses. Mapping populations are usually created from F1 lines that are derived from two parents that show differing phenotypes for a target trait.

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Decisions on selection of parents and mating design for development of mapping population and the type of markers used depend up on the objectives of experiments, availability of markers and the molecular map.

The parents ofmapping populations must have sufficient variation for the traits of interest at both the DNA sequenceandthephenotypelevel.

Types of mapping populations F2 populationF2 derived F3(F2:F3) populationsDoubled haploids (DHs)Recombinant Inbred Lines (RILs)Near-isogenic Lines (NILs).

F2 population

F2 populationBest population for preliminary mappingProduced by selfing or Sib mating the individuals insegregating populations generated by crossing the selected parents.F2 individuals are products of single meiotic cycleRatio expected for dominant markeris 3:1 and for co-dominant marker is 1:2:1F2 populations cant be easily preserved because F2 plants are frequently not immortal.

F2:3 population construction

F2derivedF3(F2:3)population F2: 3 population is obtained by selfing the F2 individuals for a single generation

Suitable for specific situations like o Mapping quantitative traits and o Mapping recessive genes

The F2: 3 family can be used for reconstituting the genotype of respective F2 plants

Doubled Haploids (DHs)

Chromosome doubling of anther culture derived haploid plants from F1 generation develops DHs.

DHs are also products of single meiotic cycle, and hence comparable to F2 in terms ofrecombination information.

The expected ratio for themarker is 1:1, irrespective of genetic nature of marker.

Double haploid lines used to avoid any residual heterozygosity.

DHs arepermanent mapping population (immortal population) and hencecan bereplicated andevaluated overlocations and years and maintained without any genotypic change.DHs Useful for mapping both qualitative andquantitative charactersSuch lines can also be obtained by colchicine treatment of haploids leading to double haploid cells. Double haploid is also an immortal population .

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Doubled haploid and RIL

Making the Intermated P1 X P2 mapping populationof recombinant inbred lines (RILs)

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Single F2 plant was selfed

Grow up 200 plants, random matingIllustration of the genotype of 6 of those 200 plants.Recombination during meiosis results in the exchange of chromosome segments

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Select 100 ears, pick 5 kernels from each ear. Put in a bag, shake, plant, more random matings (2nd generation).Repeat, (repeat.)

From these lines, generate Recombinant Inbred lines by repeated selfing (5x or more)

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x the Recombinant Inbred mapping population

Recombinant Inbred Lines (RILs)

RILsareproducedbycontinuousselfingprogeny ofindividual members of an F2 population until complete homozygous is achievedRILs also equalize marker types like DHs, the genetic segregation ratio for both dominant and co-dominant marker would be 1:1.Self fertilization via single seed descent method .Once homozygosity is achieved, RILs can be propagated indefinitely withoutfurthersegregation

Since RILs are immortal population , they can be replicate over locations and years and therefore are of immense value in mapping QTLs.

RILs being obtained after several cycles of meiosis, are very useful in identifying tightly linked makers.

RIL populations obtained by selfing have twice the amount of observed recombinationbetween very closely linked markers as compared to population derived from a single cycle of meiosis.

Zamir and colleagues at the Hebrew University made RILs between Solanum lycopersicum (domestic tomato) and Solanum pennellii. They identified 25 QTLs for soluble solids measured as Brix value. One QTL improved Brix by 10-20%. Mapping showed it to map to a chromosome region that encodes a fruit specific invertase. Fine mapping narrowed it down to a SNP in a 484 bp region of the invertase. In one specific place S. pennellii has a D (Asp) - in common with invertases from carrot, tobacco, potato and pea, but the S. lycopersicum invertase has an E (Glu)The enzyme has a higher affinity (lower Km) for sucrose and is more efficient at unloading sucrose in the fruit.Science, 305: 1786-9 (2004)

Make recombinant inbred lines (RILs) and identify quantitative trait loci (QTLs) for Brix value.GluAspBrix = refractive index and measuresmostly sugars.

NILs

Near-Isogenic Lines (NILs)NILs are generated either by repeated selfing or backcrossingtheF1 plants tothe recurrent parents(inbred parental lines).NILs developedthroughbackcrossingare similar torecurrent parent butfor thegene ofinterest, while NILs developed though selfing are similar in pair but for the gene ofinterest (however, differ a lot with respect to the recurrent parent).

Expected segregation ratio of the markers is 1:1 irrespective of the nature of marker.

Like DHs and RILs, NILs are also immortal mappingpopulation.

NILs are quite useful in functional genomics

Directly useful only for molecular tagging of the gene concerned.

APPLICATIONS

Analysis of segregation of markers.Selection of linkage groups.Map construction genetic distances.( recombination distance between loci.)

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