This document discusses different types of mapping populations used in genetic mapping. It describes F2, backcross, double haploid, recombinant inbred line, and near isogenic line populations. For each type, it provides details on how they are developed and their advantages and disadvantages. It also discusses how marker segregation ratios differ depending on the population type and marker dominance. The document recommends using short-term mapping populations initially for preliminary mapping but developing long-term populations like recombinant inbred lines for global mapping projects.

1. MAPPING
POPULATION
 PRESENTED BY :
SRISHTI AGGRAWAL
 M.SC BOTANY
 DEPT.OF SCIENCE
 DEI,AGRA
 PRESENTED TO :
 Dr. Ajay Kumar
 DEPT.OF SCIENCE
 DEI,AGRA

2. INTRODUCTION
 Population used for mapping the genes, is
commonly called as mapping population
and they usually obtained from controlled
crosses.
 Selection of parents is the 1st step for
production of mapping population.
 Parents selected to develop mapping
population should have sufficient variation for
trait of interest both at DNA sequence level
and at phenotypic level.

3.  Higher the variation, it is easier to find the
recombination.
 Mapping population is developed from
parents that are highly homozygous
 Both monogenic and polygenic traits can
be mapped when two parents are extremely
different for these traits.

4. TYPES OF MAPPING POPULATION:
 F2 progenies
 Backcross progenies (BC)
 Double haploids (DH)
 Recombinant inbreed lines (RIL)
 Near isogenic lines (NIL)

7. F2 POPULATION
 The simplest and rapid method of a mapping
population .
 Usually two pure lines are selected as
parents.
 Crossing of such parents will lead to produce
fertile progenies called F1 progenies.
 Individual of F1 plant is then selfed to
produce F2 population. Thus,F2 populations
is the outcome of one meiosis.
 The segregation ratio for codominant marker
is 1:2:1 while segregation ratio for each
dominant marker is 3:1.

8. Merits:
 Developed with minimum efforts
 Best for preliminary mapping
 Require less time for development
Demerits:
 Outcome of only one meiotic cycle
 Not immortal population

9. DOUBLE HAPLOIDS (DH)
 DH lines contain two haploid set of
chromosomes in their cells.
 DH lines are produced from haploid lines.
 In some haploid plants the chromosome no.
doubles spontaneously that lead to DH lines.
 Also obtained artificially by colchicine
treatment of haploid plants.
 In DH all markers segregate in 1:1 ratio.

10. Merits:
• Immortal/ permanent population
• Used in mapping of both qualitative and
quantitative trait
• Fast production of homozygous lines, thus
saving time.
Demerits:
• High cost involved in establishing tissue
culture.
• Recombination from the male side alone is
accounted.

11. BACK CROSS POPULATION (BC)
 To analyse the specific genes or other regulatory DNA
elements derived from one parent(donor) in the
background of another parent (recurrent),the hybrid F1
plant is backcrossed to recurrent parent.
Merits:
 The elite combination is not lost
 Less time require to develop
Demerits:
• Cant used for quantitative traits
• The recombination information in BC is based on only
one parent
• Not immortal

12. RECOMBINANT INBREED LINES (RIL)
RILs are the homozygous selfed or sibmated progeny of the
individuals of an F2 population.
Single seed descent method is best for development.
RILs with more than 98% homozygosity are produced by selfing
within 8-9 generations. Segregation ratio of RILs is 1:1.
Merits:
• Immortal population ,they can be replicated over different
locations
• Product of many meiotic cycles so useful to identify tightly linked
markers
Demerits:
• Require many seasons to develop RILs
• RIL development is difficult in crops having high inbreeding
depression.

13. NEAR ISOGENIC LINES (NILS)
NILs can be developed by repeated selfing or
backcrossing of F1 with recurrent parent.
Irrespective of dominant or codominant marker
NILs segregate in 1:1 ratio.
Merits:
 Immortal population
 Used for fine mapping
Demerits:
 Many generations require to develop NILs
 Increased cost, time and efforts

14. Combining Markers and Populations
 The genetic segregation ratio at maker locus is
jointly determined by the nature of
marker (dominant / codominant) and types of
mapping populations.
 Markers such RFLPs, microsatellites
and CAPS etc. are codominant in nature, while
AFLP, RAPD, ISSR are often scored as dominant
markers.
 F2 population segregates in 1: 2: 1 ratio for a
codominant marker and in 3:1 ratio for dominant
marker. Depending upon the segregation pattern,
statistical analysis of marker data will vary.

15. Choice of Mapping Populations
 It is evident from the foregoing discussion that
the short-term mapping populations such
as F2, backcross and conceptual NILs
developed through BSA approach can be a
good starting point in molecular mapping, while
 long-term mapping populations such
as RILs, NILs and DHs must be developed and
characterized properly with respect to the traits
of importance for global mapping projects.

16. As a matter of fact, the development and
phenotypic characterization of mapping
populations should become an integral part
of the ongoing breeding programmes in
important crops. At this point, the role of
geneticists and plant breeders becomes
crucial to reap the benefits of genetic
mapping.