Linkage mapping genetic mapping

1. MOLECULAR MARKER
TECHNOLOGY
[BTF 311]
SUBMITTED TO:- DR. NEELESH KAPOOR
SUBMITTED BY:-
SPARSH RASTOGI (5584)
SANGAM KUMAR MISHRA ( 5585)
SANKET GANGWAR ( 5625)
NANDNI SINGH (5626)

2. TOPIC :–
LINKAGE MAPPING

3. CONTENT
 Introduction
 History
 Procedure
 Types of linkage mapping
 Molecular markers used in linkage mapping
 Mapping population
 Advantages
 Disadvantages

4. INTRODUCTION
 Linkage mapping is a genetic mapping technique used to
identify the relative positions of genes on a chromosome.
 It relies on the principle of genetic linkage, where genes
located close to each other on a chromosome tend to be
inherited together.

5.  By analyzing the frequency of co-inheritance of genetic
markers, linkage maps can be created to show the order and
distances between genes, providing insights into the genetic
architecture of an organism.
 This approach is particularly valuable in understanding
inheritance patterns and locating genes associated with
specific traits or diseases.

6. HISTORY
 The concept of genetic linkage was introduced by Thomas
Hunt Morgan in the early 1910s through his work with fruit
flies (Drosophila melanogaster
 The first linkage maps were developed in the 1930s and 1940s
by Alfred Sturtevant, a student of Morgan, and Hermann
Muller. They created maps of the relative positions of genes on
Drosophila chromosomes based on the frequency of
recombination (exchange of genetic material) between genes.

7.  In the 1920s and 1930s , researchers like Raoul A. Blanchard
made efforts to map genes in wheat and barley
 The 1950s and 1960s saw the significant progress in mapping
genes in maize . Pioneering work by scientists like Barbara
McClintock, whom won a nobel prize for her research on
transposons in maize .
 The seqencing of the rice genome , completed in 2002,was a
landmark achievement that facilitated more advanced linkage
mapping in rice .

8.  The introduction of molecular techniques, such as DNA
markers, in the latter half of the 20th century significantly
improved the precision and efficiency of linkage mapping.
With the advent of technologies like polymerase chain
reaction (PCR) and DNA sequencing, researchers were able
to identify and analyze specific DNA sequences to create
more detailed and accurate linkage maps.

9. PROCEDURE
 STEP 1:--
Crossing Over: Perform a cross between two individuals that differ in specific traits.
This generates a hybrid organism with a mix of genetic material from the parent
organisms
 STEP 2:-
Selection of Progeny: Allow the hybrid organism to produce offspring (progeny).
Select individuals with the desired traits for further analysis.
 STEP 3:--
Genotyping: Analyze the genetic makeup of the selected progeny. This can be
done using molecular markers or observable traits, depending on the organism.

10.  STEP 4:--
Marker Mapping: Identify molecular markers (like DNA sequences) that are associated with the
traits of interest. These markers serve as indicators of specific gene locations.
 STEP 5:--
Data Collection: Collect data on the inheritance patterns of the markers and traits within the
progeny. This involves observing how often certain markers and traits are inherited together.
 STEP 6:--
Linkage Analysis: Determine the degree of linkage between markers and traits. Calculate the
recombination frequency, which represents the likelihood of genetic material being exchanged
between linked genes during crossing over.

11.  STEP 7:--
Map Construction: Based on the recombination frequencies, construct a
linkage map that represents the relative positions of genes on a
chromosome. Closer genes are less likely to be separated by recombination,
while genes farther apart are more likely to undergo recombination.
 STEP 8:--
Interpretation: Interpret the linkage map to understand the order and
spacing of genes on the chromosome. The unit of measure is typically
centimorgans (cM), representing the percentage of recombinant offspring.

12.  STEP 9:--
Validation : Validate the linkage map by conducting additional crosses
and analyses . This helps ensure the accuracy and reliability of the map .
 STEP 10:--
Refinement : Refine the map as more data becomes available. Additional
crosses and markers can improve the resolution and precision of the
linkage map .

14. TYPES OF LINKAGE MAPPING
 COMPLETE MAPPING:-
Complete linkage is a hierarchical clustering method where the
distance between two clusters is determined by the maximum
distance between any pair of their individual elements. In other
words, it considers the most dissimilar pair of data points, one from
each cluster, and uses that maximum dissimilarity as the distance
metric between the clusters. This approach tends to produce
compact, spherical clusters in the dendrogram.

15.  INCOMPLETE MAPPING:-
Incomplete linkage is a hierarchical clustering method where the
distance between two clusters is determined by the minimum
distance between any pair of their individual elements. In this
approach, the closest (most similar) pair of data points, one from
each cluster, is considered, and that minimum distance is used as the
distance metric between the clusters. Incomplete linkage tends to
form clusters with elongated shapes in the dendrogram.

17. MOLECULAR MARKER USED IN
LINKAGE MAPPING
Molecular markers commonly used in linkage mapping include :--
 Restriction Fragment Length Polymorphisms (RFLPs)
 Simple Sequence Repeats (SSRs)
 Single Nucleotide Polymorphisms (SNPs)
 Amplified Fragment Length Polymorphisms (AFLPs)
These markers serve as identifiable genetic landmarks, allowing researchers
to track their inheritance patterns and map the relative positions of genes
on chromosomes

18. MAPPING POPULATION
 A population that is suitable for
linkage mapping of genetic
markers is known as mapping
population. Mapping
populations are generated by
crossing two or more
genetically diverse lines and
handling the progeny in a
definite fashion. Generally, the
parents used for hybridization
will be from the same species.

20. ADVANTAGES
 Identification of gene order
 Measuring genetic distance
 Understanding linkage disequilibrium
 Map construction
 Marker Assisted selection
 Identification of Diseased genes

21. DISADVANTAGES
 Limited Resolution
 Time consuming
 Assumption of crossover equivalence
 Dependence on family size
 Limited to mendalian inheritance

22. REFERENCE
 www.biotech.article .com
 Open journal of plant science
 Slide share
 Molecular marker in crop improvement – Indian institute
of pulse research, kanpur