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Linkage analysis
Nasir Mehmood
Roll No:117102
Linkage analysis
Linkage analysis is statistical method that is used to
associate functionality of genes to their location on
chromosomes.
Neighboring genes on the chromosome have a tendency
to stick together when passed on to offsprings.
Therefore, if some disease is often passed to offsprings
along with specific marker-genes , then it can be
concluded that the gene(s) which are responsible for the
disease are located close on the chromosome to these
markers.
Linkage Analysis

Linkage analysis is a method that is used
in establishing the carrier status of female
'at-risk' carriers and for prenatal diagnosis.
In many cases, linkage analysis has been
replaced by mutational analysis but in a
small number of families in whom the
mutation cannot be identified, linkage
analysis remains the only method for the
genetic diagnosis of carriers.

Two genetic loci are said to be in linkage
if the alleles at these loci segregate
together more often that would be
expected by chance that is the two loci
are so close together on the same
chromosome that the chances of them
separating by a crossover event
(recombination) during Meiosis is small.

The probability that any two alleles at two
randomly selected loci with be inherited
together is 0.5. If two loci are closely
linked then the chances of a crossover or
recombination event occurring is <0.5.
The chances of recombination taking
places is linked to the distance between
any two loci.
 The recombination fraction is a measure
of the genetic distance between two loci.
 The distance between two loci is
measured in centimorgans


1 centimorgan is defined as the genetic
distance between two loci with a
recombination frequency of 1%. Although
the centimorgan is not a measure of
physical distance, it typically equates to a
physical distance of one million base pairs
Aim of linkage analysis

The aim of linkage analysis is to identify a
marker that co-segregates with the gene
of interest and so can be used to track the
gene within a family without actually
knowing the mutation. By definition this
marker must co-segregate with the gene
of interest and so be present in affected
family members but absent in unaffected
family members.
Chromosomal theory of Linkage:
Linked genes are located on homologous
chromosomes
 The linkage of genes is linear .this shows
that the genes themselves are arranged in
a line inside the chromosomes
 Genes situated closely in chromosomes
posses strong linkage while the linked
genes situated farther from each other
show week linkage

Example of linkage analysis

we usually think of linkage analysis using
DNA markers, other markers such as
proteins can be also be used. Such a case
is the gene for Glucose-6 Phosphate
Dehydrogenase [G6PD] which maps to the
long arm of the X-chromosome at Xq28
close to the gene for factor VIII [F8].
References
//www.illumina.com/applications/detail/sn
p_genotyping_and_cnv_analysis/linkage_a
nalysis.ilmn
 /practicalhaemostasis.com/Genetics/linkage_analysi
s1.htmlhttp://practicalhaemostasis.com/Genetics/linkage_analysi
s1.html
 Genetics book by Dr.Ali Muhammad
